Primary Mucosa-Associated Lymphoid Tissue Lymphoma of the Breast with Synchronous Contralateral Invasive Breast Cancer: A Case Report.

Primary breast lymphoma is a rare malignant breast tumor, accounting for <1% of all breast cancers. Among them, diffuse large B-cell lymphoma is the most common histologic subtype. However, primary mucosa-associated lymphoid tissue (MALT) lymphoma is less common and more indolent than diffuse large B-cell lymphoma, and primary MALT lymphoma of the breast is extremely rare. We report a case of bilateral breast cancer in a 62-year-old woman with primary MALT lymphoma in right braest and contralateral invasive breast cancer in left breast. The patient presented with a palpable right breast lump, which appeared as a noncalcified mass on mammography and an indistinct irregular hypoechoic mass with internal vascularity on breast ultrasonography. The mass was pathologically confirmed by excisional biopsy as primary MALT lymphoma. The patient underwent dynamic contrast-enhanced breast MRI, which additionally detected a small suspicious mass in the left breast. This was a clinically and mammographically occult breast cancer diagnosed as invasive ductal carcinoma.