Cerebral metastases in extrapulmonary cell carcinoma. Implications for the use of prophylactic cranial irradiation

Extrapulmonary small cell carcinoma (EPSCC) is a rare disease. Standard treatment is performed in analogy to small cell lung cancer; however, due to the differences in rates of cerebral metastases (CM), prophylactic cranial irradiation (PCI) is not routinely used. Therefore, we evaluated the characteristics of all patients developing brain metastases in a population of EPSCC patients and calculated a number needed to treat (NNT) for the prevention of cerebral metastases by PCI.

Of 51 patients treated at our institution from 1999-2011 for EPSCC, 11 presented with CM, 5 at initial diagnosis, 6 in the course of their disease. Median overall survival after primary diagnosis of EPSCC was 12 months. Overall survival after diagnosis of CM was significantly in favor of primarily cerebrally metastasized patients with 9 compared to 2 months for secondary CM (p = 0.04), median survival for all patients being 4 months. The NNT calculation was based on the 6 patients with secondary brain metastases in our series and a relative risk reduction of 60% observed in the studies of PCI for small cell lung cancer (SCLC), resulting in an NNT of 13.

Although the frequency of brain metastases in EPSCC was lower than in SCLC, the NNT of 13 for the prevention of CM, as well as the poor median survival after diagnosis of secondary brain metastases of 2 months might be a reason to discuss and evaluate PCI for EPSCC patients responding to initial therapy.