Malignant transformation of breast fibroadenoma to malignant phyllodes tumor: Long-term outcome of 36 malignant phyllodes tumors

Background: Malignant phyllodes tumor of the breast is a rare neoplasm for which clinical findings remain insufficient for determination of optimal management. We examined the clinical behavior of these lesions in an attempt to determine appropriate management. We evaluated long-term outcome and clinical characteristics of malignant phyllodes tumors arising from fibroadenomas of the breast. Methods: A total of 173 patients were given a diagnosis of phyllodes tumor and underwent surgery at the Cancer Institute Hospital in Japan between January 1980 and December 1999. Of these patients, 39 (22.5%) were given a diagnosis of malignant phyllodes tumor; in three of these cases, detailed medical records were lost. Malignant phyllodes tumors were classified into two groups based on history of malignant transformation. Of the 36 malignant cases, 11 (30.6%) were primary and were given a diagnosis of fibroadenoma, experienced recurrence during the follow-up period, and were diagnosed with malignant phyllodes tumor (cases with a history of fibroadenoma). The other group was defined as cases without history of fibroadenoma and in whom lesions initially occurred as malignant phyllodes tumors. Based on differences between the two groups, overall survival curves were plotted using the Kaplan-Meier method, and statistical comparisons were performed using the log-rank test and Peto and Peto's test. Results: The outcome of cases with history of fibroadenoma was significantly better than that of cases without history of fibroadenoma. Conclusions: Patients with malignant phyllodes tumors but without prior history of malignant transformation who exhibit rapid growth within 6 months require aggressive treatment.