Login to Access Video or Poster Abstract: MP55-01
Sources of Funding: Funded in part by the Sidney Kimmel Center for Prostate and Urologic Cancers and the National Cancer Institute Training Grant T32 CA082088 (BM, MG)

Introduction

In 2016 the World Health Organization coined the term mixed epithelial and stromal tumor family (MESTF) to encompass adult cystic nephroma (ACN) within the classification of mixed epithelial and stromal tumors (MESTs) on the basis of overlapping clinical and pathologic profiles. MESTs have traditionally been regarded as benign, with only a few reports of malignant transformation or recurrence in the literature. Diagnosis requires histopathological evaluation, as radiologic imaging cannot accurately determine whether such tumors are benign or malignant. We aim to characterize our institutional experience with this rare neoplasm.

Methods

We identified all patients with a pathological diagnosis of MEST or ACN from our prospectively collected institutional database between Jan 1995 - Dec 2015. Available imaging was re-reviewed by a single expert radiologist (AH). Demographic, radiologic, and clinical characteristics were recorded.

Results

Data was available for 40 patients. The median age at diagnosis was 48.8 years (31.5-73.4). Thirty-seven (92.5%) patients were female and three (7.5%) were male. Imaging was available for re-review for 29 (72.5%) patients. The mean diameter of the tumor on preoperative imaging was 5.8 cm (1.9-16.1). Patients presenting with symptoms at diagnosis had a mean diameter of 7.4 cm (4-16.1). On imaging, 25 (86.2%) tumors where characterized as Bosniak 3 lesions and four (13.8%) were described as Bosniak 4 lesions. All patients underwent surgical resection, with partial nephrectomy performed in 72.5% of cases. Mean pathological tumor size was 5.9 cm (1.5-15). Median follow-up was 71.6 months (1-217). Two (4.9%) patients died from non-tumor related causes. At last follow-up, all patients showed no evidence of disease.

Conclusions

MESTF are indolent tumors with a female predominance. They are usually detected incidentally as Bosniak 3 or 4 lesions. Partial nephrectomy should be performed whenever possible to resect the tumor and preserve renal function. Given the low likelihood of recurrence following excision, we believe that, once pathologically identified, patients have an excellent long-term prognosis and require minimal surveillance imaging on follow-up. Genomic characterization is currently underway.

Funding

Funded in part by the Sidney Kimmel Center for Prostate and Urologic Cancers and the National Cancer Institute Training Grant T32 CA082088 (BM, MG)