Aim: Phyllodes tumor are rare fi broepithelial neoplasms that account for less than 1% of all breast neoplasms. They usually present as fast growing, clinically benign lesion. They usually occur in middle-age women (40-50 years). At mammography or ultrasound, phyllodes tumors mostly present as well-circumscribed oval or lobulated lesion similar to fi broadenoma. A diagnosis is made by histopathologic tumor analysis which shows biphasic characteristi cs: epithelial and stomal component. The analysis of the stromal component is crucial as the stromal component determines its malignant potenti al. A phyllodes tumor can be diffi cult to disti nguish from a proliferati ve fibroadenoma at core needle biopsy so fi nal histopathologic classifi cati on requires surgical excision. Malignant phyllodes tumors with heterologous components are extremely rare. Case report: We present a case of 35-year-old woman who had excisional biopsy of both breasts due to fi broadenomas 5 years ago. On the last ultrasound exam, a newly developed lesion of the right breast was detected with benign morphologic characteristi c so a fi ne needle aspirati on was performed. At breast examinati on, a fi rm, mobile mass was palpated, without signs of local ti ssue infi ltrati on. Based on the obtained fi ndings, a benign lesion was considered so excisional biopsy of the enti re lesion was performed. Conclusion: The authors present a rare case of a young pati ent with previous excision biopsies due to multi ple fi broadenomas who developed a recurrent tumor with benign clinical characteristi cs. The patohistological analysis showed that it was a case of malignant phyllodes tumor with heterologous liposarcomatous diff erenti ati on manifesti ng as a collision tumor adjacent to a complex fi broadenoma.