Metastasis of invasive ductal breast cancer in the subcutaneous tissue of the back: Report of a relapse at 15 years.

Introduction And Importance: Soft tissue metastases from any primary malignant tumor are considered very rare and can be found in subcutaneous or muscle tissue. We present the fifth case of breast cancer (BC) metastasis in subcutaneous tissue of the back and with an interval of 15 years between its detection and the diagnosis of BC.

Case Presentation: A 57-year-old woman with a history of left mastectomy with axillary lymphadenectomy and immediate breast reconstruction due to invasive ductal BC with positive hormone receptors and HER2 negative 15 years ago. She consulted for a mass on her back and elevated levels of CA15-3. Nuclear magnetic resonance showed a tumor in the subcutaneous tissue in contact with the muscular aponeurosis. Radical metastasectomy was performed with curative intent and intraoperative control of the margins by freezing. Histopathology and immunohistochemistry reported a lesion consistent with breast adenocarcinoma metastasis, with positive estrogen and progesterone receptors, positive GATA-3, negative HER2, and free margins. The patient is free of disease 4 years after surgery.

Clinical Discussion: The incidence of soft tissue metastasis of breast cancer is 0.2-0.8 %. To date, only four cases of BC metastasis in the subcutaneous tissue of the back have been reported. This is the case with the longest relapse time reported in the literature.

Conclusion: Soft tissue metastases should be suspected in all patients with a history of breast cancer, even 15 years after diagnosis.