Thread by @smlungpathguy

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

#pathology #pulmpath

1/
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

2/
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 😜

3/
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”)

https://twitter.com/smlungpathguy/status/780943116714979328?s=21

4/
✴️ 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

5/
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

6/
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.

https://twitter.com/smlungpathguy/status/731720827008258048?s=21

However, carcinoid tumors can also occur in the periphery of the lung.

7/
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:
ncbi.nlm.nih.gov/m/pubmed/21043…

8/
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...

https://twitter.com/konzult_/status/817274100569804800?s=21

9/
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

10/
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 😅

11/
What else can look like typical carcinoid tumor in the lung?

✳️ Glomus tumor
pulmonarypath.org/cotm/2017/sep/…

✳️ Sclerosing pneumocytoma
pulmonarypath.org/cotm/2017/jul/…

Both are negative for NE markers

✳️ Small cell carcinoma
ncbi.nlm.nih.gov/m/pubmed/15644…

Here you need morphology!

12/
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

13/
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

14/
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:

15/
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”