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Sanjay Mukhopadhyay @smlungpathguy
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Tweetorial on carcinoid tumor of the lung. I’ll add to it little by little every week 😊

#pathology #pulmpath

Carcinoid tumor is the lower grade end of the spectrum of neuroendocrine tumors in the lung.

Caution: lung terminology is different from GI tract terminology
In the lung, the terminology is
✴️ Typical carcinoid tumor
✴️ Atypical carcinoid tumor
✴️ Small cell carcinoma
✴️ Large cell neuroendocrine carcinoma

We don’t terms such as “well differentiated NET” because...this is #pulmpath and we are special 😜
Carcinoid tumors are very similar on H&E to low grade NE tumors in the GI tract or pancreas. Nesting, odd patterns, bland cytology, granular chromatin (“salt and pepper”)

✴️ Most carcinoid tumors in the lung are typical carcinoids
✳️ you can’t tell typical from atypical carcinoids on cytology or in small biopsies
✴️ In these specimens, calling them “carcinoid tumor” is fine
✳️ In resections, you can tell typical from atypical
Criteria for typical vs. atypical carcinoid tumor:
✴️ Mitoses (2/10 HPF is the cutoff)
✳️ Necrosis (none in typical, “punctate” in atypical)
✴️ Either one of these is sufficient for the label of atypical carcinoid

Do NOT differentiate these based on atypia or mets
Grossly, carcinoid tumors often look a bit yellow and tend to be located within a bronchus or adjacent to a bronchus. Post-obstructive mucus plugs are common.

However, carcinoid tumors can also occur in the periphery of the lung.
One of the best reviews of neuroendocrine lung tumors was written in 2010 by my friend Dr. Natasha Rekhtman in @ArchivesPath

It’s a must-read. Here’s the link:…
Atypical carcinoid tumors are more aggressive clinically than typical carcinoids. Both can metastasize to hilar/mediastinal nodes (even rarely to distant sites) but this is more common with atypical carcinoids. So this is why we count mitoses...

What do typical and atypical carcinoids have in common?
✳️ Low grade cytology
✴️ Absence of extensive necrosis
✳️ Almost always positive for synaptophysin and chromogranin
✴️ Less than 10 mitoses per high power fields (usually far less!)
✳️ Treated surgically
What is the #ihcpath profile of a typical carcinoid tumor?
Synaptophysin +
Chromogranin +
CD56 +
Cytokeratin + (try CAM5.2 if AE1/AE3 is neg)
TTF-1 weakly + or neg
p40 neg

Do you need to do #ihcpath in every case? No, but I get synaptophysin and chromogranin in most 😅
What else can look like typical carcinoid tumor in the lung?

✳️ Glomus tumor…

✳️ Sclerosing pneumocytoma…

Both are negative for NE markers

✳️ Small cell carcinoma…

Here you need morphology!
Another tumor that many worry about but shouldn’t: paraganglioma

✅ Yes, they can look like carcinoid tumors

✅ But primary paraganglioma of the lung is vanishingly rare. Carcinoid is common. When your hear hoofbeats, think 🐎not 🦓

✅ if in doubt, get a pankeratin
Back to atypical carcinoids. Since punctuate necrosis is such a key criterion, you should know what it looks like. It can be very focal and easy to miss. It usually contains necrotic nuclei, kind of like a florid form of apoptosis

@chriszioga @pathnoob
What is the prognostic difference between typical and atypical carcinoid tumors? Per WHO:

5y survival 90% for typical carcinoid tumor, 60% for atypical carcinoid tumor

Remember: both can metastasize to nodes, although more with atypical

Data from our center are similar:
Here’s an example of a lymph node metastasis from an atypical carcinoid tumor. Nodal involvement is a significant adverse prognostic factor.

References: PMID 14698535 and 11296182
@virenkaul @leticiakawano
Sorry for typo: “punctate”
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