Abstract P5-12-08: The effect of adjuvant endocrine therapy adherence on breast cancer prognosis according to age group
Authors: Lee Yura , Kim Hee Jeong , Kim Sun Ok , Lee Jong Won 
Published: March 2020

Background: It is well known that the young age at the diagnosis of breast cancer is a bad prognostic factor, by many previous studies. In a study of breast cancer adherence to adjuvant endocrine therapy (AET), younger patients were found to have significantly lower adherence. Therefore, the poor prognosis of young patients, with hormone receptor positive breast cancer, should be figured out whether it is due to the difference in adherence. And we aimed to analyze the effect of medication adherence for 4.5 years on subsequent prognosis, after the treatment completion.

Methods: A total of 5,928 patients with stage I~III hormonal receptor positive breast cancer, who underwent surgery at Asan Medical Center from January 1997 to December 2009 were included in this retrospective analysis. Patients with no history of AET, follow-up loss, early breast cancer recurrence within 4.5 years from initial treatment were excluded. The number of days of treatment gap was estimated by subtracting the duration of medication coverage from the intervals between prescription dates. A descriptive analysis of prescription gap according to age distribution was done. And a multivariate Cox regression for the risk of distant metastasis of breast cancer by AET adherence, grouped by; no gap, gap1, gap2 (gap1: prescription gap within median, gap2: gap over median) according to age group (grouped by the age at diagnosis of &lt;40, 40~59, and ≥60), was conducted.

Results: The AET adherence was best in the middle-age group, showing the smallest number of days in treatment omission (130.9/4264, mean of total prescription gap/number of patients), compared with young (194.9/959) or old group (159.4/705). When adjusted with cancer stage, histologic grade, adjuvant treatment of chemotherapy or radiation therapy, type of AET agent, the risk of distant metastasis with increasing gaps tended to increase in the younger age group but it showed no significance between three gap-groups (p=0.063). The risk was significantly increased in the older age group, that the hazard ration (HR) in gap1 group was 2.534 (95% CI: 0.845~7.599, p=0.097), and 3.820 (95% CI 1.485~9.828, p=0.005) in gap2 group. With the reference of middle-age-no gap group, younger-no gap group showed significantly high HR (1.853, 95% CI: 1.008~3.407, p=0.047). In older age groups, only gap2 group showed significantly high HR (2.605, 95% CI: 1.443~4.703, p=0.001). However, in the risk of distant metastasis, the interaction between the gap and age difference was not statistically significant (p = 0.487).

Conclusion: In distant metastasis after AET completion, both adherence and age at diagnosis showed a strong correlation. This suggests that survival after 4.5 years in young patients could be more affected by other factors (besides compliance with medication). This implicates that the prophylactic effect of AET after the end of the routine medication period is less significant. Further analysis including patients with early recurrence is needed in the future.

Citation Format: Yura Lee, Hee Jeong Kim, Sun Ok Kim, Jong Won Lee. The effect of adjuvant endocrine therapy adherence on breast cancer prognosis according to age group [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-12-08.