Is the extension of adjuvant hormone therapy for breast cancer justified?

Abstract

In practice, all patients with ER (+) primary breast cancer should conduct adjuvant hormone therapy to suppress the growth of tumors stimulated by estrogens. Five-year tamoxifen treatment reduces breast cancer mortality for 30%, and aromatase inhibitors (for postmenopausal women) reduces it by up to 40%. After five years, long-term relapses still occurred, the risk of which can be reduced by the expansion of adjuvant hormone therapy for more than 5 years. At the population level, the treatment can show relatively moderate and sometimes toxic effects; therefore, it is extremely important for modern clinical practice to identify patients with risk of relapse within the first five years small enough for the therapy to be safely canceled for this period, as well as patients with a risk of relapse high enough to justify a longer treatment. Currently, little data is available from clinical trials regarding the second problem. Recent EBCTCG studies have consistently shown a risk of relapse within 5–20 years in all patient groups. However, the risk varies greatly depending on the size of the tumor and the status of the lymph nodes. The tumor grade (G) and the proliferation index (Ki67), supplementing the information on the TN stage, demonstrate a high degree of correlation between each other. The only patients who have a relatively low frequency of long-term recurrence (which allows them to be assigned to a very low risk group) are patients with a low tumor grade pT1N0. Prognostic molecular signatures have been proven to be clinically useful (in addition to clinical and morphological characteristics) in identifying patients with an extremely low risk of relapse who can safely avoid chemotherapy. In clinical trials of adjuvant hormone therapy with a long follow-up period (up to 20 years), a delayed (over five years) recurrence of estrogen-receptor-positive (ER+) breast cancer was noted. Based on these observations, a number of researchers offer longer hormone therapy (exceeding the five-year standard).