MS 13.04 The Role of Chemotherapy in the Management of CNS Metastasis

Abstract

The optimal management of patients with CNS metastases from lung cancer should be a multidisciplinary approach which encompasses supportive therapy, local CNS-directed therapies including surgery, stereotactic radiosurgery (SRS) and whole brain radiotherapy (WBRT), and most importantly systemic therapy. In the case of patients with small cell lung cancer (SCLC), both the primary tumor and systemic metastases are generally chemosensitive, at least initially. Most studies suggested that brain metastases are as sensitive to systemic chemotherapy as extracranial disease. The concept of the brain as a pharmacologic sanctuary site for established metastases is in contrast with clinical observations of frequent responses in brain metastases to systemic chemotherapy. Response rates (RRs) of brain metastases from SCLC to systemic chemotherapy in treatment naive patients have been reported to range from 27% to 85%. RRs in previously treated patients with brain metastases range from 22% to 50% and are comparable to the RRs with second-line chemotherapy observed in extracranial disease. A meta-analysis of five studies with a single chemotherapy for pretreated patients showed RRs ranging from 33% to 43%.1 Adding WBRT to chemotherapy increases the RR of the brain metastases, but does not appear to improve survival as shown in a phase III trial by the European Organization for Research and Treatment of Cancer.2 For patients with advanced non-small cell lung cancer (NSCLC) without molecular drivers, chemotherapy is the mainstay of treatment. Although NSCLC is less responsive to systemic chemotherapy than SCLC, results of combining platinum compounds and third generation agents are substantially better than with earlier regimens. Platinum-based doublets are the cornerstone treatment in the first-line setting for metastatic NSCLC.3 There is a presumed lack of effectiveness of systemic chemotherapy in CNS metastases from NSCLC because of the belief that chemotherapeutic drugs cannot cross the blood-brain barrier (BBB).4 However, there is increasing evidence that the integrity of the BBB is impaired and disrupted in the presence of macroscopic CNS metastases. Despite a low penetration of the CNS, chemotherapy drugs have demonstrated encouraging activity against CNS metastases from NSCLC. A number of phase II studies reported RRs to cisplatin-based combination chemotherapy regimens ranging from 35% to 50%. Several clinical trials with upfront platinum-based chemotherapy have shown intracranial RRs ranging from 23% to 50% which correlated with and almost comparable to systemic RRs.5 These data suggest that the intrinsic sensitivity of the tumor to the cytotoxic drug is more important in predicting response to the chemotherapeutic drug than the theoretical expected ability of the drug to penetrate the BBB. There are few randomized phase III trials of advanced or metastatic NSCLC evaluating different kinds of treatment in patients with brain metastases because generally, such patients have been excluded from clinical trials because of poor prognosis. Despite a penetration of CNS of less than 5%, pemetrexed demonstrated a consistent activity against brain metastases from NSCLC. One of the first evidence of pemetrexed activity against brain metastases came from a retrospective Italian study by Bearz and colleagues on 39 NSCLC patients with CNS metastases treated with pemetrexed as second or third line.6 Although the patients were unselected for histology, the study reported an intracranial RR of 30.8%, with clinical benefit obtained in 69% of patients. All patients who had an overall response (i.e., partial response and stable disease) to pemetrexed had a benefit over cerebral metastases as well with partial response in 11 patients (28.2%) and stable disease in 21 (53.8%), with a clinical benefit rate of 82% for CNS metastases and an overall survival (OS) of 10 months. The addition of platinum compounds to pemetrexed slightly improved the outcome as shown in subsequent studies. In a phase II trial on 43 chemotherapy naïve NSCLC with brain metastases (93% with non-squamous histology) treated with pemetrexed and cisplatin for six cycles, the intracranial RR was 41.9%.7 A comparable intracranial RR of 40% was observed when pemetrexed was combined with carboplatin in an observational study on 30 patients with adenocarcinoma and brain metastases.8 These clinical trials showed that platinum-based regimens are active against brain metastases from NSCLC and high RRs can be achieved with pemetrexed-containing regimens in patients with non-squamous NSCLC. A post-hoc analysis of a large prospective observational European study on 1,564 patients with newly diagnosed advanced NSCLC receiving first-line platinum-based regimens showed that in the subgroup of 263 patients with brain metastases the median OS was 7.2 months which ranged from 5.6 months for patients treated with cisplatin/gemcitabine up to 9.3 months for those treated with platinum/pemetrexed.9 In conclusion, systemic chemotherapy is an important part of the multidisciplinary management of CNS metastases. Patients with small asymptomatic brain metastases from SCLC and NSCLC should be treated with the most active platinum-based combination chemotherapy upfront. Radiation therapy and other CNS-directed treatment may be deferred until the effects of the systemic chemotherapy on the CNS metastases can be determined.