Histopathological Downgrading of Borderline Phyllodes Tumor in a Young Patient Following Chemotherapy: A Case Report.

Phyllodes tumors (PT) are fibroepithelial neoplasms that are treated by complete surgical excision. The effectiveness of adjuvant therapies, including radiotherapy and chemotherapy, for PT remains unclear, and the use of neoadjuvant chemotherapy (NAC) is yet to be established. We report a case of a 15-year-old girl with acute lymphatic leukemia (ALL) who was incidentally diagnosed with a 50-mm borderline PT in the left breast using computed tomography, ultrasonography, and histological examination following needle biopsy. Lumpectomy was performed after administration of anthracycline-based chemotherapy for ALL, resulting in tumor size reduction. Histopathological examination of the excised specimen demonstrated decreased mitotic activity and stromal cellularity post-chemotherapy. To our knowledge, this is the first study to report the histopathological differences in pre- and post-chemotherapy borderline PT samples. Our findings suggest that NAC may induce changes in borderline PT, potentially affecting diagnosis and treatment decisions. Hence, further investigation is warranted in this regard.