Biopsy of Secondary Angiosarcoma Arising in Native Mastectomy Skin of a Reconstructed Breast Without Prior Radiotherapy.

Secondary breast angiosarcoma usually develops after radiotherapy or in the setting of chronic lymphedema. We report a rare case of non-radiation-associated secondary cutaneous angiosarcoma arising in the native mastectomy skin overlying a reconstructed breast after immediate tissue expander placement and delayed deep inferior epigastric perforator flap reconstruction for breast cancer. The patient's clinical course, imaging, histopathological findings, and treatment were retrospectively reviewed. The clinicopathological features were compared with previously reported cases of angiosarcoma arising after breast reconstruction without radiotherapy before angiosarcoma onset. A 45-year-old woman underwent right mastectomy, axillary dissection, and immediate tissue expander placement for right breast cancer (T2N1M0, stage IIB), followed by delayed deep inferior epigastric perforator flap reconstruction 1 year later. No adjuvant radiotherapy was administered. Three years after the initial breast cancer surgery, progressive purpura and dark violaceous nodules developed in the native mastectomy skin. Skin biopsy confirmed cutaneous angiosarcoma. Histology showed atypical endothelial proliferation forming irregular vascular channels; tumor cells were positive for ETS-related gene and cluster of differentiation 34; the molecular immunology borstel-1 index was approximately 40%; and MYC proto-oncogene expression was observed in 60%-70% of tumor cells. Positron emission tomography-computed tomography showed no distant metastasis. Because the cutaneous disease was diffuse and surgical local control was judged difficult, multimodal treatment with pazopanib and radiotherapy (70 Gy) was initiated, followed by trastuzumab plus paclitaxel for local progression. No distant metastasis was present at the latest follow-up, although local control remained challenging. Persistent or progressive dermatitis-like lesions in postmastectomy breast skin should prompt early biopsy even in patients without prior radiotherapy.