Morning chronotype is a protective factor against chemotherapy-induced hot flashes in premenopausal women with breast cancer.

Purpose: Adjuvant chemotherapy in patients with breast cancer often causes hot flashes, impairing quality of life. However, the chronobiological or psychiatric factors associated with the development of chemotherapy-induced hot flashes (CIHFs) remain undetermined. The purpose of this study was to investigate whether chronotype was associated with the incidence of CIHFs.

Methods: A total of 119 premenopausal women with non-metastatic breast cancer awaiting adjuvant chemotherapy after surgery without hot flashes were included. The presence of CIHF was defined as having moderate to severe hot flashes, as measured by the subscale of hot flashes in the Menopause Rating Scale, at 4 weeks after the completion of chemotherapy. Chronotype (Morning/Intermediate/Evening) was assessed with the Composite Scale of Morningness before adjuvant chemotherapy. To examine the association between chronotype and CIHF, we built logistic regression models, adjusting for age, body mass index, sleep quality, and radiation therapy.

Results: CIHF occurred in 50.4% of participants. Morning type was inversely associated with CIHF (reference: Intermediate type, odds ratio [OR], 0.37; 95% confidence interval [CI], 0.16-0.94; p = 0.040) in the univariate model, and the association remained significant (OR, 0.37; CI, 0.13-0.96; p = 0.045) after adjusting for age, body mass index, sleep quality, and radiation therapy.

Conclusions: Morning chronotype is a protective factor against the development of CIHF in patients with breast cancer. Chronotypes should be assessed and considered in the prediction and management of CIHF.