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SEER Inquiry System - Report
Produced: 02/11/2026 2:22 PM
Question 20240072
Inquiry Details
References:
#1: Solid Tumor Rules. Head and Neck, 2024 Update
#2: SSDI Manual. v3.1; Appendix A
Question:
Solid Tumor Rules/Histology--Oropharynx: How is histology coded for a 2024 squamous cell carcinoma of the tonsil when immunohistochemistry (IHC) stains are negative for p16, but in situ hybridization (ISH) testing is positive for human papilloma virus (HPV)? See Discussion.
Discussion:
The Solid Tumor Rules state that for cases diagnosed in 2022 and forward, p16 testing CAN be used to assign histology code 8085 (squamous cell carcinoma, HPV positive). The rules also state that for cases diagnosed prior to 1/1/2022, code 8085 MUST be based on ISH testing and not p16. ISH testing is not specifically addressed for 2022+ cases, but are we correct in assuming it can still be used as the basis for 8085?
Multiple CAnswer Forum posts and the AJCC 8th edition Head and Neck staging webinar indicate that the correct chapter/registry staging schema in this situation is determined ONLY by p16 results - not ISH testing, and therefore the Schema Discriminator 2 SSDI should be coded as 1 – p16 negative, regardless of ISH results.
While we understand that histology codes should not be changed based on staging criteria, there is a SEER/NAACCR edit, “Schema Discriminator 2, Head and Neck, Histology (NAACCR)” tag number N6802, that will not allow coding 8085 if Schema Discriminator 2 is coded as 1 (p16 negative). The edit does seem to be correctly enforcing the AJCC guidelines for choosing the staging schema, based on the sources noted above. Do the Solid Tumor or Site-Specific Data Items (SSDI) guidelines need to be modified for this situation?
Answer:
Assign histology as squamous cell carcinoma, HPV positive (8085) for tonsil, NOS (C099) based on the positive HPV test. Codes 8085 and 8086 are valid for a select group of sites. The histology terms and codes that are valid for head and neck sites are included in the Head and Neck Solid Tumor Rules, Table 5 (oropharynx).
HPV detection tests that are used to identify HPV include DNA polymerase chain reaction (PCR), p16 (IHC), or DNA/RNA in situ hybridization. Assign the appropriate method of detection in the SEER data item, SEER Site-Specific Factor 1.
Schema Discriminator 2 captures additional information needed to generate AJCC ID and Schema ID for some anatomic sites as stated in the SSDI Manual. For oropharyngeal cancer, a schema discriminator is used to discriminate between oropharyngeal tumors that are p16 positive, p16 negative, or p16 status unknown in order to assign the appropriate schema ID. Only the HPV p16 test can be used to assign Schema Discriminator 2. If another HPV test is performed, code 9. Override the edit for Schema Discriminator 2 when p16 is negative. Coding updates will be implemented in 2025.
