Carcinoma of the Collecting Ducts of Bellini

Definition

High grade renal adenocarcinoma arising in medulla of the kidney, with a predominantly invasive tubular growth pattern
Clearly overlaps morphologically and immunophenotypically with medullary carcinoma but the latter has a distinctive clinicopathologic setting

Metastatic adenocarcinoma must be ruled out in every case
- Collecting duct carcinoma should be considered a diagnosis of exclusion
Firm mass centered on the renal medulla
- Frequently extends into renal cortex and/or pelvis
Infiltrating tubular or tubulopapillary pattern
- Occasionally solid or microcystic
- Usually single layer of lining cells with hobnail nuclei
- Extra-renal and vascular invasion frequent
- Cytoplasmic mucin may be present
  - Signet ring cells seen in rare cases
- Rare sarcomatoid cases
  - Defined by presence of a distinct spindle cell component occupying at least one microscopic low-power field (×40)
Prominent stromal desmoplasia
- Frequent mixed acute and chronic inflammation
High grade nuclear atypia
- Equivalent to Fuhrman 3 or 4
- Frequent mitotic figures
- Dysplastic epithelial lining frequently seen in adjacent collecting duct
Cases described as low grade collecting duct carcinomas in the past are better classified as one of the following
- Mucinous tubular and spindle cell carcinoma
- Tubulocystic carcinoma
Renal medullary carcinoma is considered a separate entity
- Considered by some reports to be a variant of collecting duct carcinoma
- Overlaps histopathologically with collecting duct carcinoma but is separated based on the following features
  - Occurrence in young patients
  - Association with sickle cell trait
  - Lack of INI1 expression (Cheng 2008) vs retention in 85% of collecting duct carcinoma (Elwood 2011)

John P Higgins MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342