Abstract
Dermatomyositis (DM) is complicated by malignancy in many cases, and cases associated with interstitial pneumonitis (IP) are reported to have a poor prognosis. We encountered a surgical case of premenopausal breast cancer that complicated IP and co-developed into DM and pneumomediastinum. The patient was 35-year-old woman examined for a chief complaint of a right axillary mass, decreased grip strength, and respiratory discomfort. After careful examination, the patient was diagnosed with DM, IP, and right breast cancer (T2, N2a, M0, and stage IIIa). Because patients with IP are treated with cyclophosphamide (CPA), EC therapy (epirubicin+CPA) was initiated as preoperative chemotherapy. However, the IP worsened and pneumomediastinum developed. Since the primary lesion did not decrease (but metastasis to the axillary lymph node shrunk), the patient underwent surgery. After the operation, the pneumomediastinum promptly disappeared and both DM and IP improved, suggesting that the DM and IP was a paraneoplastic syndrome of breast cancer.
