Lung Cancer Diagnosis and Classification Flashcards
How do cell pathologists contribute to molecular pathology?
They assess the sample quality for sequencing, mark the tumour area for an appropriate FISH assay, and correctly score and interpret molecular predictive assays like HER-2, ALK and PD-L1 IHC.
How does size of sample impact the purpose for the sample?
Small biopsies are for diagnosis. Resections or whole organs or parts of organs are for curative purposes.
As well as size of sample, what else do histo want from a sample?
Fresh sample, and the right site.
Molecular tests need a minimum amount of tumour content to work. What does IHC require though?
A minimum number of tumour cells.
When doing a PD-L1 ICH assay, how many viable tumour cells do you need?
100
What do you need to identify tumour cells for IHC?
Know the assay and tissue well. avoid necrotic tissue
Using IHC to test for ALK rearrangements doesn’t have a minimum of 100 cells like PD-L1 IHC. Why?
Just need enough tumour cells to see a positive result, don’t need a percentage. Will see a strong brown signal or you won’t. PD-L1 is more patchy
If you’ve seen a dark brown stain for ALK IHC, how can you confirm a rearrangement?
FISH with break apart probes. Look for a split signal, or isolate red signal.
When pathologists were surveyed about what makes their job difficult, what were the 3 most common answers?
83% - Lack of tumour content
42% - Lack of funding for staff for sectioning
33% - Lack of clinical information
What’s the issue of a pathologist that causes them to do lots of tests? And what’s a negative result of that?
If they get a negative result for a stain, they feel like they need to do more stains until they do come to a diagnosis. But an extended IHC panel being pushed to meet turn around time will use up too much tissue. Leaving little for molecular tests.
A pathologist should know what about each test like sanger and NGS?
The sample input requirements. Number of sections and thickness.
If there’s enough tumour cellularity across a whole block/section what does not need to be done
No need to do a H&E and mark the section if it’s clearly enough.
What should be specified by pathology when sending a section to genetics?
The tumour content
What doing somatic tests, what might you need to be careful of when sending samples to genetics?
If you have a germline sample then don’t send that by mistake.
What test often needs tumour and normal tissue?
Mismatch repair testing
What’s the typical tumour content required for DNA NGS assays?
> 30% tumour content
What samples are often retrieved from advanced lung cancer patients/
Small biopsies or cytology specimens such as pleural fluids or fine needle aspirates - These can be spun down and treated as a block
What two tissue features can interfere with assays and should be ideally avoided?
Mucin and necrotic tissue
When it comes to tumour content estimation, small specimens can lead to….
false negatives
What do tumour cells look like typically in lung cancer?
Big epithelial cells with big nuclei
Why should you not just look at cell area?
Because tumour cells are a lot bigger then lymphocytes, so you would largely overestimate the tumour cell content if you do it by area and not nuclei
Where especially will lymphocytes outnumber tumour cells?
In lymph nodes, so be careful
What are 3 elements responsible for the variation between observers calculating cellularity?
Inadequate definition of tumour cellularity.
Spatial heterogeneity of tissue.
Subjective character of morphological assessment.
In a study comparing lung and colon tumour cell content estimates of 40-50 participants, what was the largest difference in estimations for the same sample?
66%!!!
What had a big impact in the study comparing pathologists estimates of the same tissues?
Dense or scattered lymphocytic infiltrates or mucinous stroma.
Do pathologists typically over estimate or under estimate tumour cell content? And why is this an OK thing?
They often under estimate, which is OK, because any negative results would be considered to possibly be false negatives and get repeated anyway.
If you get 2 blocks from a core biopsy, the one with the highest neoplastic content should be conserved for which test? IHC or mutation testing?
Mutation testing.
In a CRC sample EQA or 2016 and 2017, 31/228 labs did not take into account what?
That the sample provided had no neoplastic cells. So they genotyped the sample wrongly as wildtype.
What’s the best method for delineating the tumour area on a slide?
Precise tumour shape outlining with a dotted line got the highest proportion of neoplastic cells.
Reporting of mutation testing should include what?
A statement of the estimated tumour cell content and whether it was adequate. If it was too low, state it could be a false negative and that another sample would be best.
ctDNA tests use what techniques typically?
ddPCR or allele specific PCR or NGS
ctDNA tests may represent what?
All sites of disease better
ctDNA can be in which forms?
shed DNA or exosomes bearing DNA
As well as tumour nuclei content, what else could also be given as a percentage?
Necrosis %
Be aware of what can be done to _______ your interpretation of your results
Be aware of what can be done to validate/confirm your interpretation of your results
Molecular test are ordered when?
Reflexly by a pathologist at the time of diagnosis OR requested by an onocologist at an MDT
When a cancer recurrence happens, what should you do?
Acquire a new biopsy
For lung cancer which 2 genes are standard to be mutation screened?
EGFR and BRAF
For lung cancer, which 3 genes are standard to be tested by IHC?
ALK, ROS1, PDL1
What genes are tested by fusion analysis with lung cancer that are important in other cancers?
NTRK fusions
