Testosterone and body composition in men after treatment for rectal cancer

Preoperative radiotherapy for rectal cancer may affect Leydig cell function. However, the diagnosis of posttreatment hypogonadism is complicated as sexual symptoms associated to hypogonadism can rely on adverse events of pelvic radiation and surgery.

The objective of this study was to investigate the association of testosterone levels and body composition. The clinical value of such an association is tested subsequently in the study population.

This was a longitudinal study with prospective registration during 2010-2012 and 1-year follow up. Men with rectal cancer stage I-III, treated with radiotherapy and surgery, were eligible, and 40 of 53 men were available for analysis.

The areas of skeletal muscle and adipose tissue were assessed on a defined section of a computed tomography at baseline and after 1 year. Androgen levels were recorded from morning blood samples.

The area of skeletal muscle was related to the level of bioavailable testosterone (P = 0.01) but not to the level of serum testosterone (P = 0.36). The subcutaneous adipose tissue was not related to testosterone levels. Men with posttreatment serum testosterone levels of 8-12 nmol/L and longitudinal loss of psoas muscle area had a significantly increased luteinizing hormone-testosterone ratio compared with those with longitudinal gain of psoas muscle.

The area of psoas muscle is related to the unbound fraction of circulating testosterone in men treated for rectal cancer. The longitudinal loss of psoas muscle in men with borderline levels of serum testosterone seems to be an androgen-related symptom associated with compensatory activation of the pituitary-gonadal axis indicating a testicular failure in this group of patients.