CNS metastasis in ROS1+ NSCLC: An urgent call to action, to understand, and to overcome
Authors: Sai-Hong Ignatius Ou, Viola W. Zhu PII: S0169-5002(19)30341-1
DOI: https://doi.org/10.1016/j.lungcan.2019.02.025
Reference: LUNG 5941

To appear in: Lung Cancer

Received date: 28 November 2018
Revised date: 11 February 2019
Accepted date: 21 February 2019

Please cite this article as: Ignatius Ou S-Hong, Zhu VW, CNS metastasis in ROS1+ NSCLC: An urgent call to action, to understand, and to overcome, Lung Cancer (2019), https://doi.org/10.1016/j.lungcan.2019.02.025

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CNS metastasis in ROS1+ NSCLC:
An urgent call to action, to understand, and to overcome

Sai-Hong Ignatius Ou1*,Viola W. Zhu1

1University of California Irvine School of Medicine, Department of Medicine, Division of Hematology-Oncology, Chao Family Comprehensive Cancer Center, Orange County, CA 92868, USA

*Corresponding author.

Sai-Hong Ignatius Ou, MD PhD
Chao Family Comprehensive Cancer Center,
Division of Hematology-Medical Oncology, Department of Medicine, University of California Irvine School of Medicine,
101 City Drive, Bldg 56, RT 81, Rm 241,
Orange, CA 92868-3298.
Telephone: 714-456-8104
Fax: 714-456-2242
E-mail address: [email protected]

Highlights

Incidence of CNS metastasis in ROS1+ NSCLC varies from studies

CNS metastasis is a major mode of progression while on long term treatment

ROS1 fusion variant CD74-ROS1 may have increased predilection for CNS metastasis

ROS1 TKIs has varying degree of efficacy in CNS metastasis in ROS1+ NSCLC

Better appreciation of treatment outcome of CNS metastasis is urgently needed

Abstract

The incidence of CNS metastasis at the time of diagnosis of and during the natural disease history of advanced ROS1+ NSCLC is largely unknown. It is generally believed that the incidence of CNS metastasis is lower in ROS1+ NSCLC than ALK+ NSCLC as ROS1 fusions are regarded as a less powerful driver mutation than ALK fusions in ALK+ NSCLC based on the longer progression- free survival of ROS1+ NSCLC patients than ALK+ NSCLC patients treated with crizotinib. Here we reviewed the incidence of CNS metastasis from prospective clinical trials and retrospective case series from primarily single institution. The incidence of CNS metastasis in ROS1+ NSCLC patients at the time of diagnosis ranged from 20% to mid 30% while the incidence of CNS metastasis can be as high as in the mid 50% range post-crizotinib indicating CNS metastasis is indeed a major morbidity for ROS1+ NSCLC patients throughout the course of treatment. To date 22 fusion partners in ROS1+ NSCLC have been reported in the literature and one report has indicated CD74-ROS1 fusion variant increased the predilection for CNS metastasis than non- CD74-ROS1 fusion variants. We reviewed reported intra-cranial activity of all preclinical and clinical development stage ROS1 TKIs and pemetrexed-based chemotherapy in ROS1+ NSCLC patients. While several ROS1 TKIs (i.e. entrectinib, cabozantinib, lorlatinib, repotrectinib) have reported intra-cranial response rates, there is no literature reporting on the intra-cranial activity of pemetrexed-based chemotherapy in ROS1+ NSCLC patients. In summary, better understanding the high incidence of CNS metastasis in ROS1+ NSCLC patients, how certain ROS1 fusion variant may increase the incidence of CNS metastasis, and any intra-cranial efficacy data of pemetrexed in ROS1+ NSCLC are all urgently needed.

Key Words: ROS1 lung cancer; CNS metastasis, ROS1 fusion variants

1.0 Introduction

With the discovery of anaplastic lymphoma kinase (ALK) rearrangement (ALK+) in non-small cell lung cancer (NSCLC) in 2007 [1,2], and the successful development and approval of 5 structurally different ALK tyrosine kinase inhibitors (TKIs) in the US [3,4], ALK+ NSCLC has become the prototypic model for drug development in targeted therapy. Additionally, it is now recognized that receptor tyrosine kinase (RTK) rearrangement/fusion is a class of actionable de novo driver mutation in NSCLC and other solidi malignancies [5,6] and more recently as one category of acquired resistance mechanism to epidermal growth factor receptor (EGFR) TKIs [7]. As the prototypic RTK fusion positive disease model, the treatment of ALK+ NSCLC has alerted medical oncologists to the high prevalence and incidence of central nervous system (CNS) metastases even during the first-line treatment with ALK TKI [8-11]. However, despite being discovered in the same year (2007) as ALK+ NSCLC [2], much less is known about the incidence and treatment out of CNS metastasis in ROS1-rearranged NSCLC patients likely due to lower overall incidence of ROS1-rearranged (ROS1+) NSCLC [12,13] and later development of ROS1 TKI with crizotinib as the only approved ROS1+ NSCLC eight years after the discovery of ROS1+ NSCLC [14]. Here we review the literature on the molecular biology and epidemiology of ROS1+ NSCLC, summarize the incidence of CNS metastasis in ROS1+ NSCLC and treatment outcome of CNS metastasis with ROS1 TKI and pemetrexed-based chemotherapy.

ROS1-rearranged NSCLC

ROS1 (c-ros-oncogene) is one of 58 human RTKs and the lone member of its own subfamily [15]. ROS1 and ALK shares extensive amino acid homology especially in the kinase domain [16] and is phylogenetically related to ALK [17]. Thus, most of the current approved or clinical stage ALK TKI have demonstrated pre-clinical or clinical activity against ROS1 with the exception of alectinib [18].

Discovery of ROS-rearranged and molecular biology of NSCLC

Transforming activity of ROS1 (known as mcf3 then) was first identified in 1984 [19] and the first ROS1 rearrangement (FIG-ROS) rearrangement was identified in a glioblastoma cell line [20]. It is not until 2007 that ROS1 rearrangement in NSCLC was reported by the Cell Signalling Technology group in the same year (2007) as ALK rearrangement in NSCLC [2] where global survey for tyrosine kinase activity in NSCLC tumors and cell lines identified CD74-ROS1 and SLC34A2-ROS1 fusion variants in NSCLC [2]. To date 20 different ROS1 fusion variants have been reported in NSCLC (Table 1) [20-35]. In contrast to AK+ NSCLC where EML4-ALK is the dominant ALK fusion variant accounting to close to 95% of ALK+ NSCLC [36], the most common CD74- ROS1 variant in ROS1+ NSCLC accounting for less than 50% of the ROS1 fusion variants [37].
However, it is likely that not all the ROS1 fusion variants described in other solid malignances

such as inflammatory fibroblastic tumor (IMT) (YWHAE-ROS1) [38], anaplastic large cell lymphoma (NFkB2-ROS1, NCOR-ROS1) [39], and in pigmented spindle cell nevus/Spitz nevus (CLIP1-ROS1, ERC1-ROS1, HLA-A-ROS1, KIAA1598-ROS1, PWWP2A-ROS1) [40] have not been
reported in ROS1+ NSCLC.

Importantly ROS1 rearrangement is generally the lone or sole driver mutation in the tumor type [41]. Thus, understanding the biology of the various ROS1 fusion variants will be important in the next decade of the development of therapy against ROS1+ NSCLC. Using the prototypic ALK+ NSCLC as a model, the difference in breakpoints of EML4 generates EML4-ALK fusion proteins with varying degree of stability [42, 43] and sensitivity to crizotinib [43-46].
Indeed, the progression-free survival (PFS) among ALK+ NSCLC patients with different EML4- ALK fusion variants differed significantly when treated with crizotinib [43-45]. As such there is a difference in the spectrum of acquired resistance mutations observed arising from different ELM4-ALK fusion variants when treated with first- or second-generation ALK TKI with the more re-calcitrant solvent front mutation G1202R arising from the less AK TKI sensitive EML4-ALK variant 3 resulting in a significant difference in PFS when lorlatinib is used after crizotinib [46]. One hypothesis that different selection pressure on the EML4-ALK fusion variants due to the difference in its intrinsic sensitivities to various ALK TKIs. Finally, Christine Lovy and her colleagues extended the importance of identifying the fusion partners in the pre-clinical setting by demonstrating differential sensitivities to crizotinib and other second and third-generation ALK TKIs according to the different fusion partners to ALK [47].

Epidemiology of ROS1-rearranged NSCLC

In most of the literature the incidence of ROS1+ NSCLC is cited to be 1-2% of NSCLC [48]. Two meta-analyses have indicated demonstrated the incidence of ROS1+ NSCLC is about 2.4% (95% confidence interval [CI]; 1.8% – 3.1%) [12] to 2.9% [13] among adenocarcinoma and 0.2% [12] to 0.6% [13] in non-adenocarcinoma. The incidence of ROS1+ NSCLC in adenocarcinoma among Asians 2.6% (95%CI: 1.7 – 3.5) and 2.1% (95%CI: 1.0 – 3.1) among Caucasian population [12].
Additionally, ROS1+ NSCLC was more commonly found in females (Odd Ratio [OR] = 1.54, 1.02 – 2.34) although the female predominance is only significant in Caucasian (OR = 1.99; 95%CI: 1.14
– 3.48) but not in Asian population (OR =1.33, 95%CI: 0.78 – 2.27) [12]. ROS1+ NSCLC is more common among never-smokers (OR = 3.27, 95%CI: 1.44 – 7.45) but interestingly the prevalence of never-smokers is much higher among Caucasian (OR = 11.98, 95%CI: 5.02 – 28.56) than among Asians (OR = 2.15, 95%CI: 0.86 – 5.38) [12]. Additionally, survey of the 860 metastatic adenocarcinomas of the lung from Memorial Sloan Kettering Cancer Center database revealed the incidence of ROS1 rearrangement is 2.6% very similar to the meta-analyses [49].

Central Nervous metastasis (CNS) Metastasis in ROS1+ NSCLC

Given the high prevalence of CNS metastasis in ALK+ NSCLC gleamed from randomized phase 3 trials [8-11, 50] and that crizotinib with its poor CSF penetration [51, 52] is the sole approved ROS1 TKI, it Is rathe surprising that is relative few published literature on CNS metastasis in ROS1+ NSCLC. Several aspects of CNS metastasis ROS1+ NSCLC remained largely unknown: the

incidence at diagnosis of advanced stage, and the cumulative incidence of CNS metastasis as patients progress on multiple lines of therapy, and the response of CNS metastasis to ROS1 TKIs and chemotherapy in particular pemetrexed-based.

Molecular biology of ROS1+ NSCLC CNS metastasis

Recently, the role of fusion partner seem may be important in determining the predilection for CNS metastasis [53]. In a study from Shanghai Chest Hospital, among 19 CD74- ROS1 patients, 31.6% had CNS metastases compare to no (0%) CNS metastasis among the 17 non-CD74-ROS1 patients (p = 0.02). This translated to a numerically higher ORR among the non- CD74-ROS1 fusions (94.1%) versus CD74-ROS1 fusion (73.7%, p = 0.18) when treated with crizotinib. The median PFS (17.6 months versus 12.6 months; p = 0.048) and OS (44.5 months versus 24.3 months; p = 0.036) were also significantly longer among non-CD74-ROS1 patients.
By multivariate analysis, the presence of CNS metastasis before crizotinib treatment was an independent factor for poorer OS (HR = 8.973, 95% CI: 1.723–46.720, p = 0.010). Worrisomely, during crizotinib treatment and the follow up period, the proportion of CNS progression was numerically higher (33.3%) among non-CD74-ROS1 patients compared to CD74-ROS1 patients (21.4%, p = 0.64) indicating potentially even with an initlal lower predilection for CNS metastasis at baseline development of CNS metastasis can catch up during crizotinib treatment whose CNS penetration property is low [51, 52]. This is first and only report that suggested particular ROS1 fusion variant may increase CNS predilection and thus should be treated as hypothesis generating that needed to be collaborated by other observational studies. A very

recent report indicated among the three most common ROS1 fusion partners have different subcellular locations. Both SLC3A2-ROS1 and SDC4-ROS1 localized to the endosomes and maximally activate MAPK pathway while CD74-ROS1 locazlied to endoplasmic reticulum and MAPK signaling is impaired. Maximally activated MAPK pathway results in more aggressive tumor [54]. Importantly, it remained to be determined if differential activation of MAPK pathway will result in difference in incidence of CNS metastasis.

CNS metastasis Incidence from prospective clinical trials

The first publication of clinical efficacy of TKI in ROS1+ NSCLC thus validating ROS1 rearrangement is a driver mutation was published in 2014 [26]. The study enrolled 53 ROS1+ NSCLC patients and was one of the expansion cohorts of the original phase 1 trial of crizotinib that was designed in 2006. At the time of the design of the trial, the potential high incidence of CNS metastasis in RTK-fusion driven NSCLC was clearly not appreciated. Thus, the incidence of CNS metastasis was not captured centrally (no mandatory requirement for brain imaging at the time of study entry) and the incidence of brain metastasis not reported [26]. Subsequently the largest prospective trial (00-1201) of any ROS1 TKI (crizotinib in this trial) which was conducted primarily in East Asians (China including Taiwan, japan, South Korea) did report the incidence of CNS metastases at baseline and on followed up (Table 2) [55]. The incidence of CNS metastasis was 18.1% at study entry by independent review. It was not reported whether the incidence of CNS metastasis increases with increased line of therapy. Furthermore, whether a particular ROS1 fusion variant had a higher predilection for CNS metastasis was not reported although all

the ROS1+ NSCLC patients were identified by reverse transcription-polymerase chain reaction (RT-PCR) which could detect 7 ROS1 fusion variants [56].
Other phase 2 study (EUCROSS) results of crizotinib in ROS1+ NSCLC conducted in Europe (Germany, Spain, Switzerland) (EUCROSS) [57] in France (AcSé) [58] did report the incidence of CNS metastasis (Table 2). Several other ROS1 TKIs: ceritinib [59], entrectinib [60- 62], lorlatinib [63, 64], repotrectinib [65], and DS6051b [66] all reported incidence of CNS
metastasis (Table 2).

Overall, the incidence of brain metastasis from prospective trial of ROS1 TKIs ranged from 20% to slightly above 40% in TKI-naïve and ranged from 30% to up to mid 50% indicating effective treatment approach that targets CNS metastasis in ROS1+ NSCLC patients is urgently needed. However, we are aware there is a selection bias on the part of both clinical investigators and even patients to preferentially to seek out and enroll ROS1 patients with CNS metastasis into ROS1 TKIs that have intra-cranial activity. Therefore, these second line or beyond ROS1 TKI single arm trials may artificially inflate the incidence of brain metastasis as part of the natural history of ROS1+ NSCLC. Nevertheless, this also reflects a huge unmet need of ROS1 TKIs with potent intra-cranial activity in the second-line setting and beyond.

3.2 CNS metastasis Incidence from retrospective studies

There are many retrospective studies in the literature investigating the clinic-, pathological-, and histological-characteristics of ROS1+ NSCLC patients but only a few have reported the incidence of brain metastasis [32, 53, 67, 69-71] (Table 2). In one of largest retrospective

analysis of ROS1+ NSCLC patients treated by various ROS1 TKIs and pemetrexed-base chemotherapy, incidence of CNS metastasis at baseline is 22.3% and increased to 45.6% during the duration of follow up [32]. Of note among the 80 patients who did not have CNS metastasis at the time of diagnosis 24 (30%) developed new CNS metastasis [32]. Another major retrospective analysis of ROS1+ NSCLC patients was published by the Massachusetts General hospital that included comparison to ALK+ NSCLC patients [67]. The incidence of CNS metastasis in ROS1+ NSCLC patients at initial metastatic diagnosis (19.4%) is significantly lower than the incidence of CNS metastasis in ALK+ NSCLC patients (39.1%) (p = 0.033) (Table 2). Furthermore, the cumulative incidence of BM in ROS1+ NSCLC (22%) is significantly lower than ALK+ NSCLC (56%, p = 0.001) among ROS1+ and ALK+ NSCLC patients without CNS metastasis at the time of diagnosis. When compared to ALK+ and RET+ NSCLC, the cumulative incidence of CNS metastasis was lowest among ROS1+ NSCLC patients, followed by RET+ NSCLC patients and with ALK+ NSCLC patients [68]. However, similar single institution retrospective analysis from University of Colorado reported contradictory findings [69]. The incidence of brain metastasis at the time of diagnosis is similar between ROS1+ (36%) and ALK+ NSCLC patients (34%). CNS metastasis was the sole and most common site of relapse among ROS1+ NSCLC patients.
Limitations of this study is the small number of patients and potential referral bias given the incidence of CNS metastasis is similar across all NSCLC with targetable driver mutation (ROS1, ALK, EGFR, BRAF, KRAS) [69]. Finally, from earlier and smaller series of ROS1+ NSCLC patients reported lower incidence of CNS metastasis [70,71]. Although known to exist, the incidence of leptomeningeal carcinomatosis in ROS1+ NSCLC patients has not been reported in the literature.

Treatment of CNS metastasis in ROS1+ NSCLC

Efficacy of first-generation ROS1 TKI against CNS metastasis in ROS1+ NSCLC

Crizotinib

From the largest study of crizotinib in ROS1+ NSCLC (OO-12-01, N = 127), the ORR in patients with CNS metastasis (73.9%, 95%CI: 51.6 – 89.8) was similar to patients without CNS metastasis (71.2%, 95%CI: 61.4 – 79.6) was similar. However median PFS was shorter in patients with BM (N = 23; 10.2 months, 95%CI: 5.6 – 13.1 months) than patients without baseline brain metastasis (N = 104; 18.8 months, 95%CI: 13.1 – NR) indicating CNS metastasis is a poor prognostic factor in ROS1+ NSCLC patients [55]. However, no separate analysis of intracranial- overall response rate (IC-ORR) or analysis of the first site of disease progression especially among patients with CNS metastasis have been reported [55]. The ORR of crizotinib in ROS1+ NSCLC was similar regardless of prior lines of chemotherapy. As described above, the pivotal trial of crizotinib in ROS1+ NSCLC did not capture CNS metastasis in the database [26].

Entrectinib

Entrectinib is an ALK/ROS1/pan-NTRK inhibitor that is currently being developed as a ROS1 and NTRK inhibitor [72]. In the 2018 STARTRK-1/-2 update, among the 23 patients with baseline CNS

metastasis at the time of study entry, 20 had measurable disease. The ORR among patients with baseline CNS metastasis was 73.9% (51.6- 89.8) is similar to the ORR among patients without baseline CNS metastasis (80%, 95%CI: 61.4 – 92.3). Specifically, the confirmed IC-ORR is 55% (95%CI: 32 – 77) with an intracranial duration of response (DoR) of 12.9 months. The median DoR for patients with baseline CNS metastasis on entrectinib was 12.6 months (95%CI: 6.5 – NE) compared to 24.6 months DoR among patients without baseline CNS metastasis (95%CI: 11.4 – 34.8). The median PFS for patients with baseline CNS metastasis on entrectinib treatment was
13.6 months (4.5 – NE) compared to 26.3 months (95%CI 15.7 – 36.6) for patients without CNS metastasis [60]. These results raised the question that even with good CNS activity, CNS metastasis is such a poor prognostic factor or ROS1 TKI with better CNS penetration is required. Understanding this observation will also have implication whether it is ethnical to randomized patients to pemetrexed-based chemotherapy [62].

Ceritinib

In the small phase 2 study of ROS1+ NSCLC patients, 8 patients had baseline CNS metastasis (measurable, non-measurable and non-evaluable). The IC-ORR among these 8 patients was 25% [59].

Cabozantinib

Cabozantinib is multi-targeted kinase inhibitor including being a ROS1 inhibitor. Activity of cabozantinib has been reported in one patient who developed a solvent front D2033N mutation on progression on crizotinib [73]. Although the patient had developed CNS metastasis on crizotinib and treated with whole brain radiation with continuation of crizotinib beyond progression, it is not known whether cabozantinib had demonstrated intra-cranial activity.
Recently intra-cranial activity of cabozantinib has been reported in 3 ROS1+ NSCLC patients who had achieved intra-cranially control after progression on crizotinib and ceritinib [74].

Brigatinib

Only 3 ROS1 patients were enrolled onto the phase 1 trial of brigatinib thence there is very limited clinical efficacy data on brigatinib as a ROS1 inhibitor [75]. Brigatinib is being investigated in a food-food interaction study that also enroll ROS1+ in addition to ALK+ solid tumors. (ClinicalTrials.gov Identifier: NCT03420742).

Ensartinib

Ensartinib (X-396) is a second generation ALK/ROS1 TKI that has shown preliminary activity in ALK+ NSCLC patients [76]. Preclinical enzymatic studies also indicated ensartinib is also a ROS1 inhibitor with an IC50 against GOPC-ROS1 of 0.98nM [77]. Ensartinib is the TKI in the ALK/ROS1

arm of the Pediatric Match trial in the US (ClinicalTrials.gov Identifier: NCT03213652). However clinical efficacy of ensartinib against ROS1+ NSCLC patients has not been reported.

Efficacy of Second Generation ROS1 TKI against CNS metastasis in ROS1+ NSCLC

Lorlatinib

Lorlatinib is a next generation ALK/ROS1 inhibitor [78]. The clinical efficacy of lorlatinib in both crizotinib-naïve and crizotinib-refractory ROS1+ NSCLC patient was recently presented [64].
Among the 19 crizotinib-pretreated patients with baseline CNS metastasis (measurable or non- measurable), the confirmed IC-ORR was 53% (95%CI: 29-76) with a median DoR not reached (95%CI: 5 months – NR). This is similar to the IC-ORR of 66.7% (95%CI: 22-96) among the 6 crizotinib-naïve ROS1+ NSCLC patients. The median DoR intra-cranially among the 19 crizotinib- refractory patients on lorlatinib has not been reached (95%CI: 5 – NR) [64].

Repotrectinib (TPX-0005)

Repotrectinib is a next generation compound that potently targets ROS1/NTRK/ALK but also the solvent front mutations arising from first generation TKIs [79]. Additionally, it has demonstrated CNS activity against ROS1 (and NTRK) [79]. In an update of the on-going phase 1 study, among the TKI-naïve patients with measurable disease (N = 3) the confirmed IC-ORR is 100% [65]. The IC-ORR among all 5 TKI-naïve ROS1+ NSCLC patients was 60%. Among the TKI-refractory

patients with measurable CNS metastasis (N = 4), the IC-ORR was 25%. Among all TKI-refractory patients with CNS metastasis, the confirmed IC-ORR was 9.1% [65]

4.2.3 DS-6051b

DS-6051b is a potent ROS1/pan-NTRK inhibitor developed by Daiichi Sankyo with an enzymatic IC50 against ROS1, NTRK1, NTRK2, and NTRK3 of 0.207nM, 0.622nM, 2.28nM, and 0.980nM
respectively [80]. Additionally, it has potent inhibitory activity against both the gate keeper ROS1 L2026M mutation and solvent-front ROS1 G2032R mutation with an GI50 of against Ba/F3 cells bearing ETV6-ROS1 constructs with these mutations (GI50 = 4nM against ETV6-ROS1 WT,
GI50 = 14nM against ETV6-ROS1 L2026M; GI50 = 64nM against ETV6-ROS1 G2032R) [80]. In

comparison the GI50 for crizotinib against ETV6-ROS1 WT, EV6-ROS1 L2026M, ETV6-ROS1 G20232R were 25nM, 147nM, and > 500nM in the same set of preclinical data [80]. Of the 15 ROS1+ NSCLC patients enrolled in a Japanese phase 1 study, 5 had CNS metastasis. Response image of 1 ROS1+ NSCLC patient with CNS metastasis was shown but the treatment efficacy of the other 4 patients were not reported [66].

Efficacy of pemetrexed-based chemotherapy

Individual case reports and retrospective case series have shown that pemetrexed-based chemotherapy has high ORR and duration of disease control in ROS1+ NSCLC patients [32, 81-

86]. The largest retrospective case series analysis of pemetrexed in ROS1+ NSCLC was from South Korea where 103 ROS1+ NSCLC patients were analyzed including 90 ROS1+ NSCLC patients treated with platinum/pemetrexed followed by pemetrexed maintenance and 58 ROS1+ NSCLC patients treated with various ROS1 TKIs and among them 39 patients received both pemetrexed and ROS1 TKIs [32]. It seems that the ORR, PFS, and OS all numerically favors TKI over pemetrexed. The ORR with ROS1 TKI was 70.7% compared to 53.3% with pemetrexed- based chemotherapy. The median PFS with ROS1 TKI was 12.7 months (95%CI: 8.1 – 21.8) while the median PFS was 8.0 months with pemetrexed-base chemotherapy (95%CI: 6.4 – 11.7). The OS of patients who received a ROS1 TKI was 64.9 months (95%CI: 26.3 – NR) while patients who did not receive a ROS1 TKI was 20.7 months (95%CI: 8.4 – 54.3). More importantly, the median OS of patients who received pemetrexed but did not receive ROS1 TKI was only 20.3 months (95%CI: 8.0 – NR) compared to 60.1 months of OS (95%CI: 25.6 – NR) for patients who received both pemetrexed and ROS1 TKI. The efficacy data of pemetrexed data on crizotinib- or TKI- refractory ROS1+ NSCLC patients is unknown.
There were 23 patients with baseline CNS metastasis and another 24 patients developed new CNS metastasis during the period of analysis, the IC-ORR of pemetrexed in CNS metastasis was not abstracted. Additionally, while the median time to CNS metastasis was 12 months it is unknown if there is a difference between patients treated with pemetrexed-based chemotherapy versus ROS1 TKIs [32].
Another large-scale retrospective analysis of 51 Chinese ROS1+ NSCLC patients indicated crizotinib achieved a higher ORR, DOR, and longer median PFS than pemetrexed-based

chemotherapy. However, the retrospective analysis did not report the incidence of CNS metastasis nor the efficacy if any on pemetrexed-based therapy post-crizotinib [85].
In an earlier and smaller retrospective analysis of European ROS1+ NSCLC patients (EUROS1), similar efficacy of pemetrexed-based chemotherapy was reported. On the EUROS study, 24 ROS1+ NSCLC patients received pemetrexed-based chemotherapy at any time during their treatment history and the ORR was 57.7% and median PFS of 7.2 months (95%CI: 4.8 – 9.6) [70]. Again, the efficacy data of pemetrexed data post-crizotinib progression was not reported and only 1 patient had CNS metastasis in the EUROS1 study. Both European and Korean retrospective analyses implicated brain metastasis is more common for patients on TKIs compared to pemetrexed-based chemotherapy likely due to progression extra-cranially as first site of progression (hence censoring) occurring in pemetrexed-treated patients as first progression. This indicated with superior extracranial efficacy the selection pressure for relapse/progression is in the CNS metastasis.

5. Summary

Despite the exhaustive review of the literature, the incidence of CNS metastasis in ROS1+ NSCLC can only be best estimated from single phase 2 arm clinical trials or single institution retrospective studies.
Generally it can be concluded that the incidence of CNS metastasis at the time of diagnosis ranged from 20% to mid 30%. About 30% of patients who had no baseline CNS metastasis

developed CNS metastasis during treatment with crizotinib. The incidence of CNS metastasis ranged from mid 30% to mid 55% among patients who had progressed on crizotinib.
ROS1+ NSCLC is a heterogeneous group of NSCLC with at least 20 different fusion partners identified. A provocative report indicated CD-74 ROS1 fusion variant has increased predilection for CNS metastasis and lower ORR and shorted PFS and OS in response to crizotinib treatment.
Crizotinib is the only ROS1 TKI approved by the US Food and Drug Administration. There are encouraging CNS activity from several ROS1 TKIs but the intracranial clinical activity of pemetrexed-based chemotherapy is nil in the literature. The high incidence of CNS metastasis in ROS1+ NSCLC patients is an unmet medical need.

6. Action Item

Analysis of longitudinal electronic medical records of large health networks such as FLARIRON which abstracts data from 39 academic practices and 261 community practices [87] that provide patient characteristics and treatment outcome of rare driver mutations in NSCLC and has been utilized by the US FDA to assess unmet treatment need after approval of immunotherapy is critically needed [88]. The presence of or lack of CNS activity of pemetrexed- based chemotherapy is critically needed to assess planning for future clinical trials for next generation ROS1 TKIs.

.

Conflict of Interest

SHI Ou has received consulting fee from Pfizer, Takeda/ARIAD, Roche/Genentech, Astra Zeneca, Boehringer Ingelheim, Spectrum pharmaceuticals.

SHI Ou has received speaker honorarium from Roche/Genentech, Foundation Medicine Inc, Astra Zeneca, Merck, and Takeda/ARIAD.

SHI Ou is a member of the scientific advisory board of TP Therapeutics, Inc. and has stock ownership in TP Therapeutics, Inc.

VW Zhu has received consulting fee from Takeda/ARIAD, Astra Zeneca, and TP Therapeutics.

VW Zhu has received speaker honorarium from Roche/Genentech, Foundation Medicine Inc, Astra Zeneca, and Takeda/ARIAD.

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Table 1. List of ROS1 fusion variants published in the literature

Number ROS1 fusion variant Reference*
1 CD74-ROS1 Rikova 2017 [2]
2 SLC34A2-ROS1 Rikova 2017 [2]
3 ERZ-ROS1 Takeuchi 2012 [21]
4 SDC4-ROS1 Takeuchi 2012 [21]
5 TPM3-ROS1 Takeuchi 2012 [21]
6 LRIG3-ROS1 Takeuchi 2012 [21]
7 GOPC (FIG)-ROS1 Rimkunas, 2012 [22]; Suehara, 2012 [23]
8 KDERL2-ROS1 Govindan 2012 [24]
9 CCDC6-ROS1 Seo 2012 [25]
10 LIMA1-ROS1 Shaw 2014 [26]; Zheng 2014 [27]
11 MSN-ROS1 Shaw 2014 [26]; Zheng 2014 [27]
12 CLTC-ROS1 TGCA 2014 [28]
13 TMEMB106B-ROS1 Ou 2015 [29]
14 TPD52L1-RPS1 Zhu 2016 [30]
15 CEP72-ROS1 Zhu 2018 [31]
16 ZCCHC8-ROS1 Park 2018 [32], Hicks 2018 [33]; Zhu 2018 [34]
17 SLMAP-ROS1 Park 2018 [32]
18 MYO5C-ROS1 Park 2018 [32]
19 TFG-ROS1 Park 2018 [32]
20 CD79-ROS1 Park 2018 [32]
21 MLL3 (KMT2C)-ROS1 Dagogo-Jack 2019 [35]
22 CTD-2021J15.1 (LINC00973)-ROS1 Dagogo-Jack 2019 [35]
*Only reference which is the first to report the particular ROS1 fusion is cited. In some cases, several references are cited when they appeared around the same time in pubmed.
CCDC6, coiled coil domain containing 6 gene; CD74, CD 74 molecule gene;
CD79, CD79 molecule gene;
CLTC, Clathrin heavy chain gene;
CTD-2021J15.1, (LINC00973, long intergenic non-protein coding RNA 973) EZR, ezrin gene;
GOPC, Golgi-associated PDZ and coiled-coil motif-containing protein gene;
KDEL R2, KDEL (Lys-Asp-Glu-Leu) endoplasmic reticulum protein retention receptor 2 gene; LIMA1, LIM domain and actin binding 1 gene;
LRIG3, leucine-rich repeats and immunoglobulin-like domains 3 gene; MLL3 (KMT2C, lysine methyltransferase 2C)
MSN, moesin gene;
MYO5C, myosin VC gene;
SDC4, syndecan 4 gene;
SLC34A2, solute carrier family 34 member 2 gene; SLMAP, sarcolemma associated protein gene; TFG, TRK-fused gene;
TPM3, tropomyosin 3 gene;
TMEM106B, Transmembrane 106B protein gene; ZCCHC8, zinc finger CCHC-type containing 8 gene;

Table 2. List of incidences of CNS metastasis of ROS1+ NSCLC in the published literature (Prospective trials and retrospective analysis)

Prospective Study
Study [references] ROS1 TKI Total Number of patients Number and percentage of brain
metastasis
Phase 1 portion
STARK-1 [60] Entrectinib 13 2/13 (15.4%)
Lorlatinib phase 1 [63] Lorlatinib 12 6/12 (50%) to 7/12 (58.35)*
Japan Phase 1 [66] DS6051b 15 5 (33.3%)-baseline
TRIDENT-1 Phase 1 [65] Repotrectinib 30 16/30 (53.3%)-study entry 5/10 (50%)-TKI-naïve
11/20 (55%)-TKI-refractory
Phase 2
PROFILE1001 [26] Crizotinib 53 NA
OO-1201 [55] Crzotinib 127 23 (18.1%)-baseline
EUCROSS [57] Crizotinib 34 NA
AcSé [58] Crizotinib 37 8 (21.6%)
Pan-Korean Study [59] Ceritinib 32 8 (25%)-baseline
1/2 (50%)-crizotinib-refractory 7/30 (23.3%)-ROS1 TKI-naive
STARTRK-2 [61] Entrectinib 32 11 (34.2%)
STARTRK-1/2 (2018 update) [62] Entrectinib 53 23 (43.4%)
Lorlatinib phase 2 [64] Lorlatinib 47 25/47 (53.2%)-study entry 6/13 (46%)-Crizotinib-naïve
19/34 (56%)-Crizotinib pre-exposed
Retrospective
EUROS1 [70] Crizotinib 31 1 (3.2%)
Samsung/Yonsei Hospitals, Seoul, South Korea [32] Multiple ROS1 TKIs 103 23 (22.3%)-baseline
47 (45.6%)-duration of follow up 30% (24/80) of patients without baseline CNS mets developed CNS
mets
Massachusetts General Hospital, Boston, MA, USA [67] Crizotinib 39 19.4%-baseline
22%-cumulative incidence in patients without brain mets initially 34%-cumulative incidence at years after initial metastatic disease
diagnosis
Shanghai Chest Hospital,
Shanghai, China [53] Crizotinib 36 6 (16.7%)-baseline
11 (30.6%)-duration of follow up
University of Colorado, Aurora, CO, USA [69] Crizotinib 33 12 (36.4%)-at initial stage IV diagnosis
Tata Memorial Hospital, Mumbai,
India [71] Criozotinib 11 0 (0.0)-baseline
*one patient was false positive ALK but whether the patient has CNS metastasis is not reported. 00-1201: Oxford Oncology-1201 trial; NA-not available