#1: Solid Tumor Rules (2018)
Source 1: 2018 Solid Tumor Rules
Solid Tumor Rules (2018)/Histology--Lung: Can the stated histology from a biomarker/immunohistochemistry (IHC) report be used for coding histology? See Discussion.
Example: Diagnosis is made on liver core biopsy path showing Metastatic carcinoma, poorly-differentiated, consistent with lung primary. Diagnosis Comment notes: Carcinoma cells are positive for CK7 and TTF-1, negative for CK20.
Subsequent immunohistochemistry report for PD-L1 testing states Liver: Metastatic adenocarcinoma consistent with lung primary. Interpretation: no PD-L1 expression.
IHC/Biomarker testing is often performed to determine treatment type, but it seems like some of the biomarkers for treatment planning are also histology specific. The Solid Tumor Rules do not address the use of biomarkers reports in the histology coding instructions.
Code this case to adenocarcinoma 8140/3. Biomarkers are often reported separately, not as part of the addendum, and can be used to code histology. This applies to cases diagnosed by metastatic site only.