Natural History of Primary Retroperitoneal Extra-Visceral Perivascular Epithelioid Cell Tumors (PEC): A Study from Transatlantic and Australasian Retroperitoneal Sarcoma Working Group (TARPSWG).

Background: Perivascular epithelioid cell tumors (PEComa) are a rare family of mesenchymal tumors that include several subtypes. There are very limited data describing the natural history of patients with extra-visceral retroperitoneal PEComas of the retroperitoneum. The aim of this study is to describe the clinical features, treatment patterns, outcomes, and diagnostic challenges of primary extra-visceral retroperitoneal or abdominopelvic PEComa over the past decade.

Patients and methods: This is a retrospective analysis of all extra-visceral, non-renal, retroperitoneal, or abdominopelvic PEComas treated at participating centers over the past 10 years.

Results: A total of 77 patients from 13 centers were included. The median age at diagnosis was 56 years (range 18-81 years); 73% were female. The median size was 9 cm. The tumor was classified as a PEComa not otherwise specified (NOS) in 55 (71%), sclerosing PEComa in 11 (15%), and angiomyolipoma (AML) in 11 (15%). Treatment intent was curative in 59 (77%) patients. Adjuvant radiation was given in five (8%) patients, and (neo)adjuvant systemic therapy was given to six (10%). Of those who did not undergo curative intent treatment, four (22%) patients had metastatic disease and three (17%) had primary unresectable disease. With a median follow-up of 26 months (2.3-147 months), 24 (40%) of the 59 patients having curative treatment had recurred. Recurrence rates differed by subtype, with 20 (37%) of the PEComa NOS group, 3 (27%) of the sclerosing PEComa group, and 1 (9%) of the AML group developing recurrence. The estimated 5-year OS of the whole cohort was 63% and 75% for the curative intent group.

Conclusions: Retroperitoneal and abdominopelvic PEComas show distinct behaviors by subtype. PEComa NOS had the highest recurrence and mortality, sclerosing PEComa showed intermediate risk, and AML was indolent. Histological classification is essential for prognosis and management.