A phyllodes tumor is a fibro-epithelial tumor with cystlike spaces and a leaflike appearance. It’s also known as cystosarcoma phyllodes (Johannes Muller – 1838).  The name originates from Phyllon (Gr), which means "leaf“. Clinically, patients complain of a large masse that has a painless rapid growth within weeks. Clinical breast examination shows a freely movable and sharply demarcated mass. The etiology is unkown. It respresents 0.3-1% of all breast neoplasms, almost exclusively in females, age between 40 and 60 years old.  It presents with a large, heterogeneous, sharply demarcated solid mass with round or cleft like cystic spaces. This is not specific and is often indistinguishable of a fibroadenoma. If there is an interval enlargement, then a core biopsy is indicated.
There are three subtypes, depending on four histological parameters; degree of stromal cellularity, cellular atypia, mitotic count/activity and the nature of the tumor borders.  The benign subtype (85-90%) has mildly increased stromal cellularity, minimal nuclear atypia, mitoses of ≤4/10 high-power fields (HPFs) and pushing borders. The borderline subtype has moderate stromal cellularity, moderate degree of cellular atypia, mitoses of 5/10-10/10 high-power fields (HPFs) and irregular margins. The malign subtype (10-15%) has marked stromal cellularity, high degree of cellular atypia, mitoses of >10/10 high-power fields (HPFs) and permeative margins.  However, it's often very difficult to differentiate benign and malignant tumors from core biopsy specimens. Mammography and ultrasound are certainly unreliable in differentiation.
The treatment is a wide local excision or a mastectomy if the lesion is very large. In contrast of the benign subtype, the prognosis of the malignant subtype is poorly defined. There is a local recurrence in 10-40% and up to 20% of the patients have haematogenous metastasis (bone, brain, lungs and lymph nodes).  The efficacy of adjuvant chemotherapy, hormonal and radiation therapy is still not clear. 
In conclusion, phyllodes tumors can be misdiagnosed as fibroadenomas on core biopsies. Phyllodes tumors should be considered when there are large masses or rapidly enlarging masses. Moreover, if there is a diagnosis of phyllodes tumor on core biopsy, it is still very difficult to differentiate between benign and malignant tumors. Therefore an excision is indicated if breast masses grows persistently regardless of the biopsy results.