C09.9
BillableMalignant neoplasm of tonsil, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C09.9 an HCC code?
Yes. C09.9 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 C09.9
For C09.9 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 C09.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C09.9 is the ICD-10-CM diagnosis code for malignant neoplasm of tonsil, unspecified. Cancer of the tonsil where the specific location within the tonsil tissue is not documented or specified in the medical record. C09.9 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, C09.9 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, C09.9 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.
This is a default code used when tonsil cancer is diagnosed but the exact anatomical site is not specified in documentation. Because C09.9 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 C09.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
Malignant neoplasm of tonsil, unspecified, is used when tonsillar cancer is diagnosed but the specific subsite within the tonsil is not documented. Given the increasing importance of HPV status and precise staging in tonsillar cancer management, coders should make every effort to obtain more specific site documentation.
Documentation Requirements
- ✓Pathology confirmation of tonsillar malignancy
- ✓Provider query documentation for specific tonsillar subsite
- ✓HPV/p16 status (essential for oropharyngeal cancer staging)
- ✓Laterality
- ✓Review of operative and imaging reports for subsite detail
Commonly Confused Codes
- •C09.0 — Tonsillar fossa; the most common specific tonsillar subsite — query provider
- •C09.1 — Tonsillar pillar; check if documentation mentions anterior or posterior pillar
- •C10.9 — Oropharynx, unspecified; even less specific — at least C09.9 identifies the tonsil
- •C11.1 — Nasopharyngeal wall; do not confuse pharyngeal tonsil (adenoid) with palatine tonsil