Fatigue, weight gain, lethargy and amenorrhea in breast cancer patients on chemotherapy: is subclinical hypothyroidism the culprit?

BACKGROUND: The purpose of this study was to prospectively observe the relative contribution of each viable mechanism such as hyperphagia, physical activity, body composition, steroid hormonal and thyroid function, fatigue scores on changes in body weight in breast cancer patients, receiving adjuvant chemotherapy.
METHODS: This was a prospective observational research design where 198 consecutive breast cancer patients receiving adjuvant chemotherapy were monitored from start to end and 6 months post-therapy on changes in anthropometics, fatigue, nutritional intake, physical activity, thyroid and steroid hormones.
RESULTS: We observed a weight gain over >5 lb in 22.2% of this patient population with a significant and progressive gain of 6.7 lb (P < 0.0001) at 6 months. Ninety four percent of all patients reported fatigue and 56% of patients reported lowered physical activity. A significant reduction in serum free and total estradiol (P < 0.0001) was observed indicative of reduction in ovarian function with 86% amenorrehic at the end of treatment. A significant reduction in mean serum triiodothyronine uptake levels (P < 0.05), in addition to a significant increase in TBG (P < 0.0001) from baseline to end of chemotherapy, was observed. In addition 20-25% of this patient group was already diagnosed with clinical hypothyroidism at diagnosis and treated. Changes in fatigue frequency and serum sex-hormone-binding globulin (SHBG) were variables significantly predictive of weight gain (P < 0.0001).
CONCLUSIONS: Cytotoxic agents may influence thyroid function in breast cancer patients contributing to and progressively worsening symptoms such as weight gain, amenorrhea, fatigue and lowered physical activity in this population. The present study indicates the value of screening breast cancer patients for thyroid function at diagnosis or pre-treatment.