Abstract
Cellular fibroadenoma (cFA), benign (BePT) and borderline phyllodes tumors (BoPT) demonstrate overlapping clinicopathologic features. We evaluated 507 cases including 91 cFA, 230 BePT and 186 BoPT. The WHO recommended morphologic criteria were used to classify cFA and BePT. BoPT was diagnosed when a tumor presented at least one of the 5 morphologic features (permeative border, markedly increased stromal cellularity, marked stromal atypia, ≥5mitoses/10HPFs, and presence of stromal overgrowth) but did not meet our recently proposed refined diagnostic criteria for malignant phyllodes tumor (PMID: 38934254). The median follow-up time was 79 months. Overall 23 (4.5%) of the 507 cases developed recurrence. None had distant metastasis or recurred as malignant phyllodes tumor. The recurrence rates were 7.7%, 2.2% and 5.9% in cFA, BePT and BoPT respectively. Of the 507 cases, younger age, larger tumor size, presence of myxoid stroma and stromal overgrowth were significantly associated with higher recurrence rate in univariate analysis (all p <0.05); in multivariate analysis, younger age and larger tumor size were significantly associated with while the other 2 variables were marginally associated with recurrence. Tumors > 6.5 cm had a recurrence rate of 13.5% vs 3.5% in tumors ≤ 6.5 cm; tumors with stromal overgrowth had a recurrence rate of 15% vs 4.1% in tumors without stromal overgrowth. In cFA, being of Hispanic race and presence of myxoid stroma were significantly associated with recurrence; in BePT, increased number of leaf-like structure and presence of myxoid stroma were significantly associated with recurrence; In BoPT, younger age and large tumor size were significantly associated with recurrence. Surgical margin status (positive vs negative) was not associated with recurrence in cFAs, BePTs or BoPTs. The recurrence rate in benign fibroepithelial lesions was low. No metastasis or recurrence as malignant phyllodes tumor was observed. Surgical margin status was not associated with recurrence rate. These results indicate the current classification does not correlate with clinical outcomes. We propose to use tumor size of 6.5 cm and/or presence of stromal overgrowth as the diagnostic criteria to classify these lesions as benign and borderline fibroepithelial lesions as they best correlate with clinical outcome. The significance of myxoid stroma warrants further investigation.
