Unclassified mucinous renal cell carcinoma, "Beyond the Abstract," by Omer A. Raheem, MD, MSc Anat, MCh Urol, MRCS; Ahmed Shabaik, MD; and J. Kellogg Parsons, MD, MPH

BERKELEY, CA (UroToday.com) - Renal cell carcinoma (RCC) with extensive mucin production is extremely rare, with only one similar case recently reported by Val-Bernal et al. as mucin-secreting clear cell RCC. A possible earlier case was reported in 1988 by Grignon et al. Renal epithelial tumors with mucin production other than mucinous tubular spindle cell carcinoma and collecting duct carcinoma with mucin production have been placed under the category of unclassified RCC in the latest 2004 World Health Organization (WHO) classification of tumors. Unclassified RCCs as a group account for 0.7% to 5.7% of all RCCs. By consensus, the histopathological features that might prompt assignment of an RCC to the unclassified subtype are as follows:

  1. composites of recognized subtypes,
  2. mucin production,
  3. rare mixture of epithelial and stromal elements,
  4. pure sarcomatoid morphology without recognizable epithelial elements, and
  5. unrecognizable cell types.

Unclassified RCC as a group is reportedly associated with unfavorable histological features and aggressive behavior.

In this comprehensive case report, we presented the case of a previously healthy 76-year-old woman with no prior significant medical or surgical problems who was referred to the University of California San Diego Medical Center for evaluation of a 5-cm right, solid, heterogeneous parenchymal renal mass suspicious for RCC, diagnosed on computed tomography urogram (CTU) as part of the evaluation of new-onset gross painless hematuria. In addition to demonstrating the right renal mass, there were the findings of right ureteral and renal pelvis filling defects with no evidence of abdominal or retroperitoneal lymphadenopathy, organomegaly, or distant metastasis. Laboratory values were all within normal limits. Rigid urethrocystoscopy and a right retrograde pyelogram were performed which did not demonstrate any mucosal lesions or any filling defects in the bladder, ureter, or renal pelvis. Cytology of urine obtained during cystoscopy revealed epithelial cell clusters with atypia without overt features of malignancy.

After appropriate, detailed counseling, the patient underwent an uncomplicated robotic-assisted laparoscopic right nephrectomy and had good functional and oncological outcomes. The patient was cancer-free at one-year follow-up. Pathological specimens revealed RCC with extensive extracellular mucin production (pT3a) with focal areas of clear cell carcinoma morphology. Immunohistochemical staining demonstrated the focal presence of smooth muscle fibers within the stroma of the tumor as well as a rich vascular network surrounding the tumor cell nests, but these were not extensive enough to suggest that the tumor was a mixed epithelial-stromal tumor.

Two published studies have previously demonstrated that unclassified RCC is associated with distinct and highly aggressive biological behavior and poor clinical outcome. Likewise, Crispen et al. from the Mayo Clinic studied 38 unclassified RCCs and concluded that although unclassified RCC is more likely to present with advanced clinicopathological features compared with clear cell RCC, there were no significant differences in overall or cancer-specific survival between the unclassified RCC and clear-cell RCC groups.

To conclude, this case report illustrates a rare subtype of mucinous RCC, which as of today is best categorized under the group of unclassified RCCs. The patient was managed in the usual fashion for treating RCC with similar functional and oncological outcomes. However, the histopathological findings of unclassified RCC can represent a pathological dilemma, particularly to pathologists as well as oncologic urologists. More importantly, this case report underpins the need for larger studies of similar pathological findings to analyze and identify its clinical and oncological predictors and ultimately determine the optimum multimodal therapeutic approach.

Written by:
Omer A. Raheem, MD, MSc Anat, MCh Urol, MRCS; Ahmed Shabaik, MD;* and J. Kellogg Parsons, MD, MPH as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

Departments of Urology and Pathology,* University of California, San Diego Medical Center, San Diego, CA USA

Unclassified mucinous renal cell carcinoma: A rare histopathological entity - Abstract

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