Examkin

Question

Difficulty: HardPathology and Biopsy Interpretation

A pathologist is reviewing core needle biopsy specimens from four different adult patients with newly diagnosed mesenchymal neoplasms. Match each characteristic microscopic and immunohistochemical or molecular description with its definitive pathologic diagnosis.

  • Monomorphic spindle cells in a dense storiform ('cartwheel') architecture deeply infiltrating subcutaneous adipose tissue; diffusely positive for CD34Dermatofibrosarcoma protuberans
  • Biphasic or monophasic spindle cell proliferation with scant cytoplasm; molecular analysis confirms a t(X;18)(p11;q11) chromosomal translocationSynovial sarcoma
  • Fascicles of uniform spindle cells with prominent perinuclear vacuolization located in the gastrointestinal muscularis propria; diffusely positive for KIT (CD117) and DOG1Gastrointestinal stromal tumor
  • Bland spindle cells separated by bands of keloidal collagen with prominent staghorn vessels; strong nuclear positivity for STAT6Solitary fibrous tumor

Answer

The correct pairings are: the storiform CD34-positive lesion is Dermatofibrosarcoma protuberans; the t(X;18) translocation lesion is Synovial sarcoma; the KIT/DOG1-positive lesion is Gastrointestinal stromal tumor; and the STAT6-positive keloidal lesion is Solitary fibrous tumor.
Each described mesenchymal tumor possesses highly specific, definitive diagnostic criteria. Dermatofibrosarcoma protuberans is characterized by CD34 positivity and a storiform pattern infiltrating adipose tissue. Synovial sarcoma is defined molecularly by the t(X;18) translocation. Gastrointestinal stromal tumors are driven by KIT or PDGFRA mutations, rendering them strongly positive for KIT (CD117) and DOG1. Solitary fibrous tumors are defined by a NAB2-STAT6 gene fusion, which is detected via strong nuclear STAT6 immunohistochemical staining alongside characteristic staghorn vasculature.

Step-by-Step Solution

1
Analyze the first description for key architectural and immunohistochemical features.
The storiform architecture infiltrating fat combined with CD34 positivity identifies Dermatofibrosarcoma protuberans.
Dermatofibrosarcoma protuberans is a locally aggressive cutaneous spindle cell tumor defined by this specific histologic pattern and immunophenotype.
2
Identify the defining molecular abnormality in the second description.
The t(X;18) translocation is identified as the defining characteristic of Synovial sarcoma.
This specific chromosomal translocation is pathognomonic and used to definitively diagnose synovial sarcoma, differentiating it from other high-grade sarcomas.
3
Evaluate the anatomic location and immunophenotype of the third description.
A gastrointestinal mesenchymal tumor expressing KIT (CD117) and DOG1 is definitively diagnosed as a Gastrointestinal stromal tumor.
KIT and DOG1 are highly sensitive and specific markers for Gastrointestinal stromal tumors, effectively differentiating them from true leiomyomas or schwannomas in the GI tract.
4
Correlate the vascular pattern and specific nuclear stain in the fourth description.
The combination of staghorn vessels, keloidal collagen, and nuclear STAT6 expression identifies a Solitary fibrous tumor.
STAT6 nuclear staining is a highly specific marker for Solitary fibrous tumor, reflecting the underlying NAB2-STAT6 gene fusion.

Key Concept

The pathologic diagnosis of mesenchymal neoplasms relies heavily on specific immunohistochemical markers (e.g., STAT6, CD117, CD34) and molecular cytogenetics (e.g., t(X;18) translocation) to differentiate tumors with overlapping spindle cell morphology.
Rate this question

Topics

Pathology and Biopsy Interpretation

More questions from this topic