Microscopic description:

The tumor on low power is well demarcated from uninvolved renal parenchyma.

The tumor cells are arranged in tightly packed, small, elongated tubules separated by pale mucinous stroma.

The areas where these tubules are arranged parallel to each other gives spindle cell appearance to the tumor.

On high power the cells show peripheral palisading, small nuclei with minimal nuclear atypia and no mitotic activity.

Few areas with papillary configuration are noted.

On high power the tumor cells are uniform, bland, low cuboidal with eosinophilic, focally vacuolated cytoplasm. 

Immunohistochemistry shows diffuse strong staining for CK7, AMACR ang negative staining for CD 10.

Discussion:

Mucinous tubular and spindle cell carcinoma is a rare (<1% of all renal neoplasms) low grade polymorphic renal epithelial neoplasm with extracellular mucinous material, tubular architecture and spindle cell areas.

They occur in wide age range, 17-82 (mean 53 year) and are more common in female with male to female ratio of 1:4.

They usually present as asymptomatic masses, often found on ultrasound (like our case).

Clinically these are indolent tumors without any known recurrences and rare incidences of metastases.

Treatment is resection.

Gross:
  • Mucinous tubular and spindle cell carcinomas are well circumscribed 2-10 cm mass (mean 4cm) with grey/light tan uniform glistening cut surfaces.

Microscopy:
  • Histologically they are comprised of bland, low cuboidal tumor cells with eosinophilic focally vacuolated cytoplasm. The cells are arranged in long tubules which transition into anastomosing spindle cells. The tumor cells are surrounded by myxoid and bubbly basophilic mucinous material. Focal collections of foamy macrophages are usually present in the stroma. Its not uncommon to see papillae with fibrovascular cores and occasionally areas of necrosis and chronic inflammation may be present.

Immunohistochemistry:
  • These tumors have a complex immunophenotype and are positive for Pax 8, EMA, AMACR, AE1/3, CK7 and are usually negative for marker of proximal nephron such as CD 10.

Molecular profile:
  • Hypodiploid with multiple chromosomal losses involving chromosomes 1, 4, 6, 8, 9, 13, 14, 15, 22.

Differentials of MTSCC:

Features that are common to both

  • Papillary growth
  • Mucin production
  • Foam cells
  • AMACR expression

Features that will help in differentiating them

Table depicting Mucinous tubular and spindle cell carcinomas
Table depicting Mucinous tubular and spindle cell carcinomas
Table depicting Mucinous tubular and spindle cell carcinomas

Differential Diagnoses of Mucinous Tubular and Spindle Cell Carcinoma (MTSCC) With Similarities and Distinguishing Features

Table depicting Mucinous tubular and spindle cell carcinomas

Nathany S, Monappa V. Mucinous Tubular and Spindle Cell Carcinoma: A Review of Histopathology and Clinical and Prognostic Implications. Arch Pathol Lab Med 1 January 2020; 144 (1): 115–118

References:

Andeen NK, Tretiakova M. Mucinous tubular and spindle cell carcinoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormalignantmucinoustubular.html. Accessed February 18th, 2022.

Nathany S, Monappa V. Mucinous Tubular and Spindle Cell Carcinoma: A Review of Histopathology and Clinical and Prognostic Implications. Arch Pathol Lab Med. 2020; 144 (1): 115–118

Shen SS, Ro JY, Tamboli P, et al. Mucinous tubular and spindle cell carcinoma of kidney is probably a variant of papillary renal cell carcinoma with spindle cell features. Ann Diagn Pathol. 2007;11(1):13-21

CASE IMAGES