C19
BillableMalignant neoplasm of rectosigmoid junction
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C19 an HCC code?
Yes. C19 maps to Bladder, Colorectal, and Other Cancers 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 C19
For C19to 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 C19 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C19 is the ICD-10-CM diagnosis code for malignant neoplasm of rectosigmoid junction. Cancer that occurs at the rectosigmoid junction, which is the area where the sigmoid colon meets the rectum. C19 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, C19 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.363. Under the older CMS-HCC V24 model, C19 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.307. 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 code is used when the tumor involves the junction between sigmoid colon and rectum. Because C19 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 C19 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code is used when the tumor involves the junction between sigmoid colon and rectum
- •Verify documentation confirms involvement of the junction area rather than just one segment
Clinical Significance
Malignant neoplasm of the rectosigmoid junction is clinically significant because tumors at this boundary zone between the sigmoid colon and rectum may require treatment approaches from both colon and rectal cancer paradigms. The rectosigmoid junction is defined as the area approximately 12-15 cm from the anal verge, and cancers here may be managed with either low anterior resection or sigmoid colectomy depending on exact location and extent. Accurate coding at this specific junction affects treatment decisions and resource allocation.
Documentation Requirements
- ✓Documentation confirming the tumor involves the rectosigmoid junction specifically
- ✓Distance from the anal verge if measured (typically 12-15 cm)
- ✓Histological type and grade
- ✓Stage of disease with circumferential resection margin status
- ✓Whether neoadjuvant chemoradiation was administered (more common for rectal-predominant tumors)
Excludes 1 — Do NOT code together
- malignant carcinoid tumors of the colon (C7A.02-)
Commonly Confused Codes
- •C18.7 — Sigmoid colon: if the tumor is entirely in the sigmoid without extending to the rectum, use C18.7
- •C20 — Rectum: if the tumor is entirely rectal without sigmoid extension, use C20
- •C21.8 — Overlapping sites of rectum/anus/anal canal: use when the tumor extends below the rectum to involve anal structures