Cytologic diagnosis of metastatic malignant phyllodes tumor of the breast in pleural effusion.

A 54-year-old woman presented with a left breast mass, discovered 4 years ago but was static until 2 months before presentation, when it showed a rapid increase in size and became painful. Mammography showed a large lobulated mass with internal cystic components (BI-RADS 4B). A biopsy was performed, followed by modified radical mastectomy. The histologic diagnosis was malignant phyllodes tumor (PT). The patient developed local recurrence 4 months later while on adjuvant radiotherapy and she had a salvage resection. Two months later, she developed massive left pleural effusion. Pleural fluid cytology showed single discohesive markedly atypical cells with hyperchromatic and enlarged nuclei, irregular nuclear membrane, and distinct macronucleoli. Multinucleated forms were also seen. The mononuclear and multinucleated tumor cells cytomorphologically resembled that of the recurrent tumor, indicative of recurrence. Positron emission tomography/computed tomography confirmed recurrence at the left pleura. The patient opted for palliative care and succumbed 1 month later. The current case demonstrated a rare clinical presentation of recurrent malignant PT as massive unilateral malignant pleural effusion. Correlation with previous histologic and cytologic specimens may be useful as similar cytologic features could be identified in subsequent recurrent tumors.