Fibroepithelial lesions of the breast: a comprehensive morphological and outcome analysis of a large series

Abstract

Mammary fibroepithelial lesions encompass a wide spectrum of tumors ranging from an indolent fibroadenoma to potentially fatal malignant phyllodes tumor. The criteria used for their classification based on morphological assessment are often challenging to apply and there is no consensus as to what constitutes an adequate resection margin. We studied a retrospective cohort of 213 fibroepithelial lesions in 178 patients (80 fibroadenomas with unusual features and 133 phyllodes tumors: 63 benign, 41 borderline, and 29 malignant) in order to describe the spectrum of changes within each group, with special emphasis on margin evaluation. Outcome data were available for 153 fibroepithelial lesions in 139 patients (median 56 months, range 3-249 months). Positive final margin (tumor transected), age < 50 years and a predominantly myxoid stroma were statistically significant predictors of local recurrence, while age > 50, stromal overgrowth, diffuse marked atypia, necrosis and mitotic index of ≥ 10 per 10 HPF were predictive of distant metastases. Tumors with satellite/bulging nodules were at a significantly higher risk to have a final positive resection margin. Our findings highlight important aspects of the interpretation and reporting of fibroepithelial lesions: the amount of myxoid stroma and the presence of satellite nodules are clinically relevant and should be routinely assessed and reported; infiltrative border might not be a prerequisite for the diagnosis of malignant phyllodes tumor, while the presence of tumor necrosis, massive stromal overgrowth or mitotic index of ≥ 25 per 10 HPF is diagnostic of malignant phyllodes tumor. On the other hand, increased mitotic index outside of the range of the World Health Organization guidelines in the absence of other worrisome features should be treated with caution, as it can be found in benign tumors.

Retrospective study of malignant phyllodes tumors of the breast: Younger age, prior fibroadenoma surgery, malignant heterologous elements and surgical margins may predict recurrence

“…Moreover, grade and LN status were not reported in more than 50% of patients in this article [ 36 ]. In agreement with previous reports [ 6 , 37 ], young age is an adverse prognostic factor for RFS in patients with MPT. Therefore, emphasis should be placed on improving the awareness of young patients on this disease.…”

Correlations of morphological features and surgical management with clinical outcome in a multicentre study of 241 phyllodes tumours of the breast

“…In the quest to identify morphological features suggestive of progressive disease, Slodowska et al analysed a series of fibroepithelial lesions, including fibroadenomas with unusual features. 34 They reported that a predominantly myxoid stroma was associated with LR, although clear defining thresholds for assessing this were not provided. They also recorded the presence of satellite nodules, which almost reached significance in terms of LR.…”

“…4 Studies on selected cohorts of malignant PTs have consistently found larger size, necrosis, and the presence of heterologous elements to be predictive. 31,34,39 Other morphological features have inconsistently been found to be associated with metastatic events across the literature; however, this is perhaps due to low numbers of these rare tumours and to differences in study designs. [13][14][15]17,22,25,34,35,40,41…”

Periductal Stromal Tumors and Phyllodes Tumors Represent a Spectrum of Fibroepithelial Lesions: What Is in a Name?

“…1 These biphasic neoplasms encompass a wide spectrum, ranging from benign fibroadenomas to frankly malignant phyllodes tumors. 2 Fibroadenomas are the most common type of fibroepithelial neoplasm and differ from phyllodes tumors as to their clinical behavior, epidemiological characteristics, and histology. Women with a fibroadenoma are generally younger.…”

“…Women with a fibroadenoma are generally younger. 2 Fibroadenomas are usually slow-growing, tend to be smaller, and have a lower propensity to recur than phyllodes tumors. 1 Phyllodes tumors present with a hypercellular expansive stroma and increased intracanalicular stromal proliferation, which gives rise to characteristic leaflike protrusions that bulge into elongated lumina.…”