Risk factors for male breast cancer - A case-control study from Scandinavia

We report a population-based case-control study on risk factors for male br east cancer. Data on a broad range of previously suggested risk factors wer e collected in a set of Scandinavian breast cancer cases and matched contro ls. Incident cases (n = 282) with histologically verified carcinomas of the breast were identified from notification to the cancer registries of Denma rk, Norway and Sweden over a 4-year period 1987-1991 and of these cases, 15 6 men could be approached and responded. Controls were identified through n ational central population registers and were matched individually for coun try, sex and year of birth. Controls with a diagnosis of breast cancer were excluded; 468 of 780 controls responded. Data on risk factors were collect ed by self-administered questionnaires mailed to the cases between land 2 y ears after diagnosis and to controls during the same period. The findings w ere compatible with an increased risk associated with family history of bre ast cancer (odds ratio (OR) = 3.3, 95% confidence interval (CI) 2.0-5.6), o besity 10 years before diagnosis (OR = 2.1, 95% CI 1.0-4.5) for BMI > 30, d iabetes (OR = 2.6, 95% CI 1.3-5.3) and the use of digoxin and methyldopa (O R = 2.0 and 2.1, respectively). The association with family history of brea st cancer has been repeated in several studies, while the relation to anthr opometric measures has been equivocal. We could not substantiate some assoc iations seen in other studies; namely those with high education, fertility, marital status, testicular injury, liver disease and religion. The detaile d questions about gynaecomastia indicated that many cases reported signs of breast cancer as a gynaecomastia, This type of misunderstanding may explai n the strong association with gynaecomastia seen in other studies. Several patients died before contact. Thus, risk factors related to a more aggressi ve male breast cancer or related to high risk of dying (e.g. liver cirrhosi s, heavy smoking) may have been missed.