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

[BACKGROUND] Trastuzumab-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.

[OBJECTIVE] To 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.

[METHODS] This 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.

[RESULTS] Among 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.

[CONCLUSIONS] Prior 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.