Locally advanced breast cancer sometimes results in a large chest wall defect at mastectomy. When closing the wound horizontally, the skin tension is usually severe in the middle of the wound, while the skin of the lateral area tends to make a dog-ear deformity. Triangle technique is a procedure to prevent the dog ear in which the skin and subcutaneous fat of the axilla are cut into an equilateral triangle. Herein, we present a case of breast cancer who underwent a mastectomy and closed the wound with a skin graft by utilizing the skin removed from lateral thoracic area using triangle technique. An 85-year-old female visited our institution complaining about the mass on her right breast. Preoperative images showed a 10 cm-sized mass with suspicious axillary and mediastinal lymph nodes swelling. A biopsy revealed a hormone receptor-negative, HER2positive invasive ductal carcinoma. A mastectomy and axillary lymph node sampling were performed for a local control as the tumor did not respond to four cycles of triweekly trastuzumab combined with S-1. After a transverse elliptical incision, a skin of the lateral thoracic area was harvested using triangle technique. As the middle of the wound had excessive closing tension, the skin was grafted on the defect. After 10 day fixation by a tie-over dressing, the wound healed without complications. This procedure is a simple method for closing a large defect after mastectomy preventing both the dog-ear deformity and a new wound scarring of a donor site.

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