Case 112
- Wangpan Shi
- May 18
- 2 min read
A 83-year-old male with history of skin carcinoma now presented left postauricular mass.
The tumor was found to be tumor to be positive for CK5/6, CK19, EMA, CD117 (patchy), and BerEP4 (patchy). Occasional tumor cells are positive for p40. Considering the history, what is the most likely diagnosis?
A: Squamous cell carcinoma
B: Porocarcinoma
C: Adenoid cystic carcinoma
D: Basal cell carcinoma
Answer
The correct answer is B. Histologic sections demonstrate nests of squamoid cells with focal ductal/glandular differentiation and comedonecrosis. EMA positivity is important to highlight the ductal features.
Loss of diagnostic features: In poorly differentiated porocarcinoma, characteristic poroid cells and cuticular cells may no longer be recognizable, complicating classification.
Mimics due to necrosis: Single-cell necrosis in other tumors may form pseudoductal structures, which can resemble porocarcinoma histologically.
Immunohistochemistry aids distinction: Use of CEA (Carcinoembryonic Antigen) and EMA (Epithelial Membrane Antigen) can help identify true ductal structures, assisting in the differentiation from mimics.
Histopathologic variability: Porocarcinoma can show squamous differentiation, clear cell change, and other atypical features, leading to a broad differential diagnosis.
Importance of identifying parent lesion: Finding a pre-existing poroma or porocarcinoma in situ is the best strategy to confirm diagnosis and avoid misinterpretation.
Immunohistochemistry
No single marker is both completely sensitive and specific for porocarcinoma.
NUT (nuclear protein in testis):
Ductal differentiation can be confirmed via:
EMA (epithelial membrane antigen)
CEA (carcinoembryonic antigen)
These may also detect abortive intracytoplasmic lumina (PMID: {6092444})
Case credit: UCSD Pathology
Author: Wangpan Jackson Shi, MD
Comments