C16.9
BillableMalignant neoplasm of stomach, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C16.9 an HCC code?
Yes. C16.9 maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lung and Other Severe 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 C16.9
For C16.9 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 C16.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C16.9 is the ICD-10-CM diagnosis code for malignant neoplasm of stomach, unspecified. Stomach cancer when the specific location within the stomach cannot be determined or is not documented. C16.9 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of digestive organs (c15-c26).
Under the CMS-HCC V28 risk adjustment model, C16.9 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, C16.9 mapped to the same category but with a base RAF weight of 0.973 — V28 recalibrated weights across the entire model. 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; attempt to obtain more specific anatomical location from pathology or imaging reports. Because C16.9 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 C16.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a default code; attempt to obtain more specific anatomical location from pathology or imaging reports
- •Use only when no other C16 code can be assigned due to lack of site specification
Clinical Significance
Unspecified stomach cancer indicates documentation does not identify the specific anatomical region within the stomach. While this code captures the same HCC as specified gastric cancer codes, it represents a documentation quality gap. Gastric cancer overall has significant mortality and morbidity, requiring complex multimodal treatment with surgery, chemotherapy, and sometimes radiation, all of which justify the high risk adjustment weight.
Documentation Requirements
- ✓Confirmed diagnosis of gastric malignancy
- ✓Review of endoscopy, imaging, pathology, and operative reports for specific site information before defaulting to unspecified
- ✓Histological type if available
- ✓Stage of disease
- ✓Current treatment status