Malignant Mesothelioma Mimicking Invasive Mammary Carcinoma in a Male Breast

Abstract

Malignant mesothelioma is an uncommon tumor with strong association with asbestos exposure. Few cases of malignant pleural mesothelioma metastatic to the female breast have been reported. Herein, we presented, for the first time, a case of locally infiltrating malignant pleural mesothelioma forming a mass in the breast of a male as the first pathologically confirmed manifestation of the disease. Breast ultrasound revealed an irregular mass in the right breast which involves the pectoralis muscle. Breast core biopsy revealed a proliferation of neoplastic epithelioid cells mimicking an infiltrating pleomorphic lobular carcinoma. IHC studies showed the cells to be positive for calretinin, CK5/6, WT1, and CK7. The cells were negative for MOC-31, BerEp4, ER, and PR. A final diagnosis of malignant mesothelioma, epithelioid type, was rendered. This case demonstrates the importance of considering a broad differential diagnosis in the setting of atypical presentation with application of a panel of IHC markers.

Figure 1

(a) Anteroposterior chest X-ray shows pleural thickening along the right lateral chest wall and blunting of the right costophrenic angle. (b) A chest CT scan shows extensive pleural thickening on the right side and calcified pleural plaque on the left side. (c) A breast ultrasound shows an irregular, hypoechoic mass measuring 5.6 × 2.9 × 3.6 cm. A portion of the mass involves pectoralis muscle and extends into the intercostal muscles. (d) Pleural biopsy shows plaque formation with dense fibrosis, minimal inflammation, and dystrophic calcification with no evidence of malignancy.

Figure 2

Histopathology and immunoprofile of the metastatic malignant mesothelioma to the breast. ((a) and (b)) Representative H&E captions from the metastatic malignant mesothelioma in the breast biopsy which show proliferation of neoplastic epithelioid cells forming cords and nests which infiltrate the breast parenchyma and skeletal muscles. The neoplastic cells are round to polygonal with moderate cytoplasm, moderate cytologic pleomorphism, and occasional nucleoli. The neoplastic cells are positive for WT1 (inset in (b)), calretinin (c), and CK5/6 (d).