Mucinous Tubular and Spindle Cell Carcinoma of the Kidney

Definition

Low grade neoplasm of the kidney composed of bland tubules set in a mucinous stroma

Composed of elongate tubules, variably packed
- Curvilinear, branching
- Range from loose, freely anastomosing spaces to densely packed side by side
- Generally locally uniform in size, although size may vary from area to area
- PASd highlights intact basement membrane around most tubules
- Focal papillary architecture has been reported
Spindle cell population merges with and may represent densely packed collapsed tubules
- Spindle cells resemble the tubular lining cells
- May vary from predominant to absent
Mucinous stroma separates the tubules
- Varies from abundant to sparse and focally absent
- Acid mucin stains positive
- Frequently vacuolated stroma
Epithelial and spindle cells are cytologically bland
- Uniform small oval nuclei
- Scant pale cytoplasm
- Focal atypia has been reported in rare cases
Occasional findings
- Collections of foamy macrophages
- Lymphocytic infiltrate
- Psammoma bodies
- Solid foci without detectable stroma
- Clear cell foci
Sarcomatoid change may be seen in rare cases
- Epithelioid or spindle cells with high grade nuclear atypia
- May behave aggressively
MTSCC may show morphologic and immunophenotypic overlap with papillary renal cell carcinoma (Paner 2006)

Features that may be shared
- Papillary growth
- Mucin production
- Foam cells
- AMACR expression
We diagnose borderline cases as papillary carcinoma
- Urologists are much more familiar with that diagnosis
- That diagnosis will probably elicit more extensive followup

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