C09.8
BillableMalignant neoplasm of overlapping sites of tonsil
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C09.8 an HCC code?
Yes. C09.8 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C09.8
For C09.8 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C09.8 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C09.8 is the ICD-10-CM diagnosis code for malignant neoplasm of overlapping sites of tonsil. Cancer that involves multiple overlapping areas of the tonsils, where the exact boundaries between different sites are unclear or the tumor spans across several tonsil regions. C09.8 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lip, oral cavity and pharynx (c00-c14).
Under the CMS-HCC V28 risk adjustment model, C09.8 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C09.8 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.306. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Use this code only when the malignant neoplasm involves two or more subsites of the tonsil and the primary site cannot be determined. Because C09.8 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C09.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the malignant neoplasm involves two or more subsites of the tonsil and the primary site cannot be determined
- •Review pathology reports to confirm overlapping involvement before assigning this code rather than a more specific tonsil site code
Clinical Significance
This overlapping tonsillar cancer code represents tumors that span multiple tonsillar subsites (fossa, pillars) where a single primary origin cannot be determined. These are typically larger tumors at diagnosis that cross the anatomical boundaries within the tonsillar region.
Documentation Requirements
- ✓Pathology and imaging confirming involvement of multiple tonsillar subsites
- ✓Documentation specifying which tonsillar structures are involved
- ✓HPV/p16 status
- ✓Laterality
- ✓Evidence that a single primary tonsillar subsite cannot be determined
Commonly Confused Codes
- •C09.0 — Tonsillar fossa; use when confined to the fossa
- •C09.1 — Tonsillar pillar; use when confined to the pillar(s)
- •C09.9 — Tonsil, unspecified; use when the specific tonsillar subsite is unknown (not when multiple sites are involved)
- •C10.8 — Overlapping sites of oropharynx; use when tumor extends beyond the tonsillar region to other oropharyngeal sites