RESUMEN
INTRODUCTION: The stromal component of Phyllodes tumors represents the neoplastic portion of the lesion. A variety of associated malignancies can arise from PTs, with its dual population of cells. PRESENTATION OF CASE: We share a very rare case of "borderline"breast phillodes tumour with a 75% liposarcoma component. A 48-year-old woman presented at the surgical clinic with a mass in the left breast. On mammograms, the lesion was dense with radiolucent areas inside which were thought to be compatible with fat. The mass was assumed to be breast imaging-reporting and data system (BIRADS) 3 on sonography as it was well contoured. The needle biopsy was reported to be consistent with a fibroadenomatous lesion. The lesion was completely excised. On microscopic examination, the lesion has benign mammary duct epithelium lining the slit-like spaces. The stroma composed of fibrous and adipous tissue. The fibrous part was cellular, and several cells appeared bizarre. Adipous tissue replaced most of the stroma and was diagnosed as pleomorphic liposarcoma. DISCUSSION: According to the 3 tiered grading criteria of PTs, our case normally suits in borderline category, without liposarcoma component. Heterologous sarcomatous elements usually accompany high grade PTs. Rare cases of benign and borderline PTs with sarcoma component have been reported. CONCLUSION: The presence of a malignant heterologous component places the tumour into the malignant category regardless of other histological features.