Objective Breast phyllodes tumors（PTs） are rare fibroepithelial tumors that are characterized by formation of foliation patterns. Behaviorally, only relatively poor prediction of PTs is possible based on their histological appearance. PTs are frequently misdiagnosed because they are difficult to differentiate from soft tissue tumors. In this report, we describe the pathological features of a rare case of PT and review the relevant literature, summarizing the essentials of the diagnosis and differential diagnosis, while attempting to avoid misdiagnosis or missed diagnosis of the tumor to the best of our abilities.Methods We present a case of pulmonary metastatic lobular tumor, analyzing the morphological [hematoxylin-eosin（HE） staining] and immunohistochemical（streptavidin perosidase method, SP） features of the tissue.Results Long spindle-shaped tumor cells were observed using microscopy. The cells were arranged in bundles, with a whirlpool pattern, and braided. The proliferation of the spindle cells was markedly atypical and karyokinesis was elevated. Residual ductal epithelium was detected in some areas, and the margins of the tumor tissues showed invasive growth. Immunohistochemical studies of the spindle-shaped tumor cells were positive for actin, PR, CD10, SMA, Bcl-2, and negative for CKP, S-100, CD34, ER. The Ki-67 index was 40%.Conclusion The spindle cell tumor identified in the lung should first be considered as a metastatic neosplasm, because most soft-tissue sarcomas commonly metastasize through the bloodstream to the lungs. Although malignant breast PTs are rare, a detailed medical history that includes prior surgical history is required to avoid wrongful or missed diagnosis.
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