Treatment patterns, health care resource utilization and costs, and clinical outcomes among older adult patients with advanced HER2-positive gastric or gastroesophageal junction adenocarcinoma.

backgroundTrastuzumab-based regimens are the historical standard first-line (1L) treatments for HER2+ advanced gastric/gastroesophageal junction (GEJ) adenocarcinoma. With pembrolizumab recently approved in combination with trastuzumab and chemotherapy as 1L treatment for patients with a programmed death-ligand 1 combined positive score of 1 or higher, establishing real-world benchmarks for patients' real-world outcomes from the preimmunotherapy era is essential.

objectiveTo assess the real-world treatment patterns and the clinical and economic impact of 1L trastuzumab-based regimens among patients with HER2+ advanced gastric/GEJ adenocarcinoma.

methodsThis retrospective study used the Surveillance, Epidemiology, and End Results-Medicare linked database (January 1, 2011, to December 31, 2019) to identify patients with HER2+ advanced gastric/GEJ adenocarcinoma who initiated a 1L trastuzumab-containing regimen (index date). Outcomes during follow-up (from index to death/data end) included health care resource utilization (HCRU), health care costs (2022 US dollars), 1L to 3L treatments, real-world overall survival (rwOS), and real-world time to next treatment or death (rwTNTD). All-cause and cancer-related HCRU and costs were assessed during preprogression, postprogression, and terminal care periods. rwOS and rwTNTD were assessed in the overall cohort and in subgroups by 1L therapy.

resultsAmong 315 included patients (mean age 73.9 ± 5.9 years; 77.1% male; 84.1% stage IV at initial diagnosis; 58.7% gastric adenocarcinoma), the most common 1L regimen was trastuzumab + chemotherapy doublet (57.8%), with the mean time to 1L initiation being 2.2 ± 3.3 months. Nearly half (49.5%) received 2L and, among them, 46.8% proceeded to 3L. Cancer-related inpatient admissions occurred among 52.9%, 64.2%, and 46.6% of patients during the preprogression, postprogression, and terminal care periods, with mean lengths of stay of 1.1, 1.1, and 3.9 days/person-month, respectively. The mean monthly all-cause total health care costs were $12,356, $13,545, and $19,085 during the above periods, respectively. In the overall cohort, median rwOS and rwTNTD were 15.3 (95% CI = 13.2-16.9) and 8.3 (6.7- 8.9) months, respectively, which varied across subgroups by 1L regimen. The trastuzumab + chemo-monotherapy subgroup was older (mean age 78 years) with median rwOS of 12.0 (95% CI = 8.3-14.9) months.

conclusionsPrior to the advent of immuno-oncology agents for HER2+ advanced gastric/GEJ adenocarcinoma (2011-2019), the economic burden was substantial throughout patients' treatment journey, whereas OS ranged from 12.0 to 15.3 months. During this period, trastuzumab with chemo-monotherapy backbones was often used in older patients. These real-world benchmarks offer valuable context for evaluating the impact of newer therapies in this population.