Tumor-to-Tumor Metastasis: An Uncommon Case of Metastatic Breast Carcinoma to Pheochromocytoma.

Background & objective: Tumor-to-tumor metastasis is a rare phenomenon in which one primary tumor metastasizes into another histologically distinct tumor. This report presents a unique case of breast carcinoma metastasizing to a pheochromocytoma, posing significant diagnostic and therapeutic challenges.

Case presentation: A 71-year-old woman with a history of breast carcinoma-status post mastectomy 7 years prior-presented with elevated levels of cancer antigen 15-3 (CA15-3), raising suspicion of disease recurrence or metastasis. Imaging studies revealed a mass in the adrenal gland. Surgical excision of the adrenal lesion was performed, and subsequent histopathological and immunohistochemical analyses confirmed the coexistence of two distinct tumor components: primary pheochromocytoma and metastatic breast carcinoma.

Conclusion: Although tumor-to-tumor metastasis is exceedingly rare, awareness of this entity is crucial for accurate diagnosis and effective treatment planning. This case underscores the importance of considering prior malignancies in the differential diagnosis of new adrenal masses and highlights the complexities involved in managing a hormone-secreting neoplasm concurrently harboring metastatic disease.