Objective: To study the clinicopathologic features of malignant phyllodes tumors (PT) by histopathologic analyses, immunohistochemical profiling and DNA content assay, and evaluation of the clinical outcome.
Methods: Ten patients with malignant PT from 1999 to 2013 who were treated by surgery were enrolled in this study. The morphologic characteristics were studied under light microscope, standard two-step EnVision method of immunohistochemical staining was used to assess the expression of CK5/6, CKpan, 34β E12, desmin, p63, ER-α, PR, Ki-67, CD34, SMA, p53, p16, bcl-2 and CD117 in the tumors. The corresponding paraffin blocks were also used for flow cytometric DNA content assay. These data were correlated with the follow-up results.
Results: The median age of onset was 46.5 years old. The mean tumor size was 7.4 cm (2.0-25.0 cm). At the end of the follow-up period (22 to 125 months), there were tumor recurrences in 3/8 patients and the median time of recurrence was 24 months. Metastasis occurred in 3/8 patients who all died of the tumors. PT had heterogeneous histology, with stromal overgrowth with leaf-like projections, periductal stromal overgrowth, and most commonly, diffuse stromal overgrowth with sarcomatous differentiation. The mean positive index of Ki-67 was 11.4%. The stromal tumor cells were positive for CD34, SMA, p53, p16, and bcl-2 in 3/10, 9/10, 6/10, 8/10, and 4/10 cases, respectively. CD117,ER-α and PR were negative. Interpretable DNA histograms were obtained in nine cases with triploidy in two cases.
Conclusions: The diagnosis of malignant PT should be considered based on the diversity of growth patterns and heterogeneous histology.Ki-67 and CD34 are valuable diagnostic and prognostic factors in patients with malignant PT. Tumors with diffuse stromal overgrowth, heterologous elements, Ki-67 ≥ 20% or aneuploidy are more likely to metastasize.