Thread by @TristanRutland7

Skin and Lymph node, adult

#dermpath #hemepath #pathtwitter #pathresidents

Based on the initial images only, what is your first impression?

Immunohistochemistry:
CK20 and CAM5.2

Chromogranin

⚕️Diagnosis:

🔬Merkel cell carcinoma

🙏Colleagues case

Question:

Merkel cell carcinomas (MCC) are associated with?

1/ MCC are more likely to occur in older patients (~70-80 yo).

2/ They are more common in sun exposed areas.

3/ MCC are associated with Merkel cell polyomavirus (MCPyV), UV radiation and immunosuppression.

pubmed.ncbi.nlm.nih.gov/28802497/

In Australia (my country), most cases of MCC are thought to be caused by?

4a/ Worldwide, MCPyV is the main culprit(~80%))

4b/ In Australia & New Zealand, most MCCs are negative for MCPyV (UV related)

5/ They are likely genetically different (virus vs UV).

6/ This raises the question, should their treatment be different?
onlinelibrary.wiley.com/doi/full/10.11…

Question:

Merkel cell carcinoma that are NEGATIVE for the MCPyV are more likely to have?

7/ The below paper found that a significant number of MCPyV negative cases showed ⬆️⬆️C>T transitions, while MCPyV positive cases didn't.

8/ Note, while suggestive of UV radiation (UV signature), C>T transitions are can be caused by other mechanisms.
ncbi.nlm.nih.gov/pmc/articles/P…

9/ Overall negative cases had more mutations.

10/ Also note, UV radiation can cause localised immunosuppression (check out the article below on photoimmunology).

jidonline.org/article/S0022-…

11/ Lastly, here is a nice summary of MCC by @ProfRScolyerMIA

https://twitter.com/ProfRScolyerMIA/status/1129506721737482240?s=20