Disparate survival trends in histologic subtypes of metastatic non-small cell lung cancer: a population-based analysis

Erlotinib, bevacizumab, and pemetrexed improved survival of metastatic non-small cell lung cancer (mN-SCLC) in clinical trials, but their benefits are restricted to non-squamous histology. We studied recent survival trends in mNSCLC subpopulations defined by histology and associated clinical factors correlating with adenocarcinoma or endothelial growth factor receptor mutations. Using the Surveillance, Epidemiology and End Results database, we calculated relative survival at 1 year from diagnosis for mNSCLC cases diagnosed in 2000-2011. Trends by histology, age, sex, race, prevalence of smoking or poverty, expressed as annual percent change (APC) using joinpoint regression, were compared by test of slope parallelism (P-par). Among 226,446 cases, 47% had adenocarcinoma, 20% squamous carcinoma, 6% other, and 27% unspecified histology. The proportion of cases designated as adenocarcinoma significantly increased after 2005. One-year survival increased from 23.5% in 2000 to 30.5% in 2010, significantly more for adenocarcinoma (APC, 3.3%) than squamous carcinoma (APC, 2.1%, P-par = 0.0018). For patients with adenocarcinoma, these trends were significantly better for Asians than Whites (P-par = 0.012) and for areas with fewer smokers (P-par = 0.014). Such differences were not observed for squamous carcinoma (P-par = 0.87 and 0.14, respectively). The absolute disparity in one-year survival between adenocarcinoma and squamous carcinoma increased from 1.6% in 2000 to 5.5% in 2010. The disparity between Asians and Whites increased from 5.2% to 13.1%, respectively. These data demonstrate that improvement in survival of mNSCLC since 2000 is now evident on a population scale. The superior increment for patients with adenocarcinoma, particularly among Asians and in communities with fewer smokers, suggests impact of the newly introduced, histology-specific agents, rather than better supportive care alone. Growing disparities between adenocarcinoma and squamous carcinoma highlight the needs to intensify research on treatment for subgroups that did not benefit from recent advances.