#1: Solid Tumor Rules (2018, 2021)
Source 1: 2018 Solid Tumor Rules
Notes: Other Sites; Updated 9/11/2018
Solid Tumor Rules (2018)/Histology--Prostate: How is the histology coded for a diagnosis of mixed prostatic adenocarcinoma (5%) and small cell neuroendocrine carcinoma (95%) from a transurethral resection of the prostate? See Discussion.
Following the existing Solid Tumor Rules Histology Rules, it would seem this is a single primary with histology 8045 (Combined small cell carcinoma) because there is no indication there are multiple prostate tumors and Table 2 states combined adenocarcinoma and small cell carcinoma is Combined small cell carcinoma (8045).
Conversely, while not an exact match to this case, SINQ 20190083 implies small cell carcinoma and adenocarcinoma of the prostate are separate primaries. In that SINQ case, the patient was simultaneously diagnosed with metastatic small cell carcinoma of the prostate on a liver biopsy and prostate adenocarcinoma on a prostate biopsy. There is no indication that patient had separate tumors in the prostate, however the SINQ instructs to code as separate primaries.
Would the previous SINQ logic apply to synchronous diagnoses in the prostate as well? Or does code 8045 apply to this situation?
Assign histology code 8045 for combined small cell carcinoma as this represents one tumor with mixed histologies using the 2018 Other Sites Solid Tumor Rules, Rule H16.