Case 10
- Wangpan Shi
- Jan 9
- 2 min read
Updated: Jan 23
A 30-year-old male with multiple lung nodules identified and here is the largest one:
differentials
Lymphoma
Small cell carcinoma
Poorly differentiated carcinoma
Alveolar rhabdomyosarcoma
You can vote for more than one answer.
Based on the differential diagnosis, a panel of stains were performed; The lesional cells are positive for TLE1 and focal weak positive for CD99 immunostain and are negative for pankeratin, SOX10, TTF-1, chromogranin, synaptophysin, CD45, Pax8, WT1, myogenin, desmin immunostains. INI1 immunostain is retained. While waiting the molecular results, how do you sign out the case?
A: Small round blue cell tumor, see comment
B: Small round blue cell tumor, favor Ewing sarcoma
C: Small round blue cell tumor, favor synovial sarcoma
D: High grade maligancy, see comment
Answer
The preferred diagnostic line in this case is small round blue cell tumor, see comment.
2. FISH showed SS18-SSX fusion, what is the final diagnosis?
Answer
Synovial sarcoma, poorly differentiated. Poorly differentiated SS showed highly cellular round cells with hyperchromatic nuclei and frequent mitotic activity and necrosis. In this case, there is around 34 mitotic figures per 10 high-power field. It is often difficult to distinguish poorly differentiated SS from other tumors such as alveolar rhabdomyosarcomas, Ewing sarcomas, and undifferentiated round cell sarcomas (previously Ewing-like sarcomas).
Lineage specific markers can be helpful: myogenin, myoD1 for ARMS, FLI, NKX 2.2 for Ewing sarcoma, BCOR, WT1, ETV4 for CIC-DUX and BCOR rearranged tumors.
By IHC, EMA is expressed more often and more widely in SS than cytokeratins, especially in monophasic and poorly differentiated subtypes It is common for poorly differentiated SS to contain focal EMA, whereas only about 50% of these tumors express cytokeratin. 40% of SSs exhibit focal S100 expression. In monophasic SS, CD34 immunostaining is rare. In most cases of SS, BCL2 and CD99 stain positive (although in Ewing sarcoma these markers may be membranous), but these markers do not indicate a specific type of SS. SSs that are biphasic, monophasic, or poorly differentiated generally exhibit moderate to strong nuclear staining for the transcriptional corepressor TLE1. There are, however, other histological mimics of SS that show TLE1 staining, in particular malignant peripheral nerve sheath tumors and solitary fibrous tumors.
References:
Case credit: UCSD Pathology
Author: Wangpan Jackson Shi, MD
Comments