Palliative Radiation Therapy For Metastatic Primary Signet Ring Cell Carcinoma Of The Lung: A Seer Analysis

Primary signet ring cell (SRCC) of the lung is an extremely rare subtype of lung adenocarcinoma with a poor prognosis. Studies have shown a prevalence of distant metastases at initial diagnosis in lung SRCC. The role of palliative radiotherapy in lung SRRC with distant organ metastases needs to evolve. We analyzed SEER data to examine the role of palliative radiation in metastatic lung SRRC. Data were obtained from SEER database between 2010-2014.Patients of interest were identified by site recode C34.0-34.9 and ICD-O-3 code 8490/3 from SEER. We recorded metastatic information related to specific-organ metastases. Overall survival (OS) was calculated from the date of diagnosis using Kaplan Meier (KM) survival analysis and Cox regression model for comparisons of hazard ratio (HR) among subgroup. A two side p value <0.05 was regarded statistically significant. A total of 242 patients with metastatic lung SRCC were included. The median age was 64. 227 patients have a single-organ site of metastases while 15 patients have multi-organ metastases. For patients with single site metastases, the proportion of bone, brain, liver, lung metastasis was 41.0%, 20.7%, 12.8%, 25.6%, respectively. The mean survival was 10.3 months (95% CI=8.4-12.2), 1-yr OS ,2-yr OS was 28.50%, 14.40%, respectively. There was significant difference in OS between single site metastatic lung SRCC patients received palliative radiotherapy (yes vs no, Mean Survival (MS) 12.4 months vs 8.5 months) (p<0.001). For patients with isolated brain metastases at diagnosis, addition of palliative radiation improved OS significantly (MS 14.9 months; 1-yr OS 49.1%; 2-yr OS 18.9%;) compared to no radiation (MS 4.9 months, 1-yr OS 7.1%; log-rank p=0.005). OS was significantly different between patients with isolated-liver metastases treated with radiation (MS 11.3 months; 1-yr OS 36.4%; 2-yr OS 24.2%) versus no radiation (MS 7.5 months; 1-yr OS 18.8%; 2-yr OS 9.4%; log-rank p=0.04). For patients with isolated bone metastases , palliative radiation didn’t improve OS significantly (MS 9.9 months; 1-yr OS 24.7%; 2-yr OS 12.4%) compared to no radiation (MS 8.8 months; 1-yr OS 25.8%; 2-yr OS 8.2%; p=0.217). For isolated lung metastases patients underwent radiotherapy, MS was 12 months, 1-yr, 2-yr OS were 45.6%, 27.3%, which was significantly different versus no radiation (MS 3 months; 1-yr OS 22.5%; 2-yr OS 14.1%; p=0.02). Multivariable analysis showed that, for isolated brain, lung and liver metastases lung SRCC patients, palliative radiotherapy was associated with longer OS compared with observation. However, treatment of radiation couldn’t improve OS for lung SRCC patients with isolated bone metastases. For primary lung SRCC patients with isolated brain, liver or lung metastases, our analysis showed OS benefit of palliative radiation. Palliative radiotherapy should be recommended for metastatic lung SRCC in clinical management.