Adenoid cystic carcinoma of the breast: truly uncommon or easily overlooked?

BACKGROUND Adenoid cystic carcinoma of the breast is an uncommon histologic form of breast cancer, comprising in most series less than 1% of all mammary cancers. Due to the rarity, little information about its presentation on image studies has been noted in the literature. Here we report two additional cases with emphasis on the intriguing image presentations. CASE ONE A 67-year-old woman came to our clinic with the chief complaint of mastodynia. No obvious palpable mass of breast was found on physical examination. Mammography showed a small well-defined nodule in the medial part of the left breast without mammographic evidence of malignancy. Ultrasonography showed a 1.5 cm nodule with well-defined margin and heterogenous echogenicity in the medial part of the left breast. Unusually, a painful sensation was experienced on compression by the probe. The final pathological report was adenoid cystic carcinoma. CASE TWO A 48-year-old woman also came to our clinic with the chief complaint of mastodynia. No obvious palpable mass of breast was found on physical examination. Mammography showed dense mammary tissue with no mammographic evidence of malignancy. Ultrasonography showed two contiguous well-defined nodules with heterogenous echogenicity in the upper, middle part of the left breast. Unusually, a painful sensation was also noted on compression by the probe. Histopathological examination showed typical features of an adenoid cystic carcinoma. CONCLUSION Adenoid cystic carcinoma of the breast fails to show the typical appearance of invasive ductal carcinoma on both mammogram and ultrasonography, probably due to its relatively well-defined nature with less surrounding architectural disruption and fibrosis. Hence a "negative" finding or a benign-looking breast lesion on mammography cannot completely exclude the existence of this disease. The presence of a painful breast lesion without obvious inflammatory evidence while compressed is a meaningful clue, which should lead to the suspicion of adenoid cystic carcinoma of the breast.