Incidental Findings of Internal Mammary Lymph Node Recurrence after Breast Cancer during Microsurgical Breast Reconstruction: Discussion of Treatment Options and Review of the Literature

Lymphatic drainage through the internal mammary lymph nodes (IMLN) is a key pathway for breast cancer metastasis, although IMLN metastasis is rare following primary treatment. In earlier years, treatment protocols primarily addressed axillary lymph node metastasis.We present five cases where IMLN metastases were discovered incidentally during autologous free-flap breast reconstruction. These cases highlight implications for both the reconstructive plastic surgeon and subsequent adjuvant therapy.From a plastic-reconstructive perspective, we recommend performing routine biopsies on any incidentally identified IMLN during autologous breast reconstruction. Positive findings may upstage the patient's disease and influence further treatment planning. However, we do not recommend actively searching for or extending dissections to harvest IMLN specimens. Only in the presence of a suspicious perinodal tumour mass do we perform an intraoperative frozen-section analysis, with reconstruction paused if malignancy is confirmed. After complete staging and discussion in a multidisciplinary conference, we proceed with tumour resection according to oncological standards if curative resection is deemed feasible. Reconstruction can then be performed during the same procedure. For locoregional recurrence of breast cancer, treatment continues to be a multimodal approach involving surgery, radiation, and systemic therapy to ensure local control and optimise long-term survival. In primary treatment, current national and international guidelines now recommend locoregional irradiation of the internal mammary chain for high-risk cases, which may further reduce the incidence of incidental IMLN metastasis findings in the future.