Quiz what is your diagnosis?

An 81-year-old man with diabetes and hypertension developed a non-tender mass in his left breast. He first palpated with a 2.5 cm-sized mass in 2018 without constitutional symptoms and did not have treatment. Two years after the appearance of the primary lesion, the size of mass was nearly 30 cm extending into the armpit with no axillary lymph node enlargement. The enhanced computed tomography and magnetic resonance imaging revealed that the tumour was of uneven enhancement, with no enhanced necrotic area in the patchy interior, and the boundary between the tumour and the left pectoralis major, serratus anterior and latissimus dorsi muscle was not clear. The patient was treated with left breast lumpectomy, and did not receive chemotherapy or radiotherapy. However, just 2 months after the surgery, a 3.5 cm tumour near the armpit reappeared. The tumour was removed again. During the operation, a 30 cm-sized, firm, grayish-white, deeply located muscle mass was resected. Haemorrhages and cyst changes were found at the site. Microscopically, the tumour was predominantly composed of spindle cells, and displayed diffusely infiltrative growth in the subcutaneous tissues. Tumour stroma was predominantly collagenous that contains thin-walled blood vessels, while focal myxoid areas were occasionally observed (Fig. 1–4).