Purpose: The association of thyroid related diseases and sex hormones with breast cancer (BC) is reported with inconclusive results. Objectives: The study was designed to analyze the thyroid/sex hormone ratios of BC patients. Methodology: TSH, T3, T4, estrogen, progesterone and testosterone concentrations of newly diagnosed breast cancer patients (n=155) aged 30 to 75 years and age-matched normal controls (n=75) were analyzed. Thyroid: sex hormone ratios were calculated. Data on history of thyroid related diseases were collected. Results and Discussion: History of thyroid related diseases was significantly higher (p

Purpose: The study intended to analyze the incidence of thyroid related diseases and to assess thyroid to sex hormones ratios of breast cancer (BC) patients Methods: TSH, T3, T4, Estrogen, progesterone and testosterone levels of newly diagnosed BC patients (n=155) aged 30 to 75 years and age-matched normal controls (n=75) were analyzed. Data on history of thyroid related diseases were collected from an interviewer administered questionnaire. Thyroid/sex hormone ratios were analyzed and compared against healthy women. Results: History of thyroid related diseases was significantly higher (p<0.05) in BC patients compared to controls. Patients (10%) with history of thyroid related diseases were excluded from the study. Subclinical hyperthyroidism was identified among 14% of the remaining BC patients and was the only dysfunction (7%) among healthy women. Significantly higher (p<0.05) mean T3 and T4 values, lower TSH levels and non-significant levels of estrogen and progesterone were observed in patients with BC when compared to healthy. Serum Testosterone of BC patients were significantly low (p<0.05). Considering the thyroid to sex hormones ratios among postmenopausal women, T3/testosterone, T4/testosterone, T3/estrogen, T4/ estrogen, ratios were significantly different in the two groups and the highest significance was found with T3/testosterone. Cutoff values studied from receiver operative characteristic curves indicated that a woman having T3/testosterone above 7.47 showed 12.5 times odds (p=0.000) of being diagnosed with BC. Conclusion: Incidence of thyroid related diseases are higher among BC patients and elevation of T3/testosterone ratio indicated a significant risk of BC. However, a study involving a larger number of participants could confirm the above.