The pathologic standards of multiple primary malignant neoplasms are : 1) Each tumor should be pathologically malignant. 2) Each tumor should be an independent malignancy, and not the result of submucosal or intraepidermal malignant changes. 3) Additional malignancies should not be metastatic. Multiple primary malignant neoplasms which have these standards have been studied continuously, no conclusive evidence for causal relationship has been established. Especially, many reports on the association of breast cancer with thyroid disease or salivary gland tumors have been published, but without any definite evidence. In 1984, Dr. Schenker, however, declared that during an 18-year study, 10,302 cases of breast carcinomas were diagnosed, and, of these, 984 patients(8%) had multiple primary malignant tumors. A significantly higher than expected incidence of second primary cancers occurred at the following five sites : the opposite breast, the salivary glands, the uterine corpus, the ovaries, and the thyroid. The authors report one example of Grave's disease and an other example of pleomorphic adenoma in breast cancer patients.