C20 ICD-10-CM Code: Malignant neoplasm of rectum
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of digestive organs (C15-C26)
C20
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant neoplasm of rectum
Cancer that develops in the rectum, which is the final section of the large intestine that connects to the anus.
Buddy Insight
Malignant neoplasm of the rectum is one of the most common colorectal cancers and has a distinct treatment paradigm from colon cancer, often requiring neoadjuvant chemoradiation followed by total mesorectal excision.
CMS-HCC V28
MappedHCC 22
RAF 0.0
CMS-HCC V24
MappedHCC 11
RAF 0.306
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 11
RAF 0.0
RXHCC
00
RAF 0
Code Trumping
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Code Book Path
Inclusion Terms
Official- Malignant neoplasm of rectal ampulla
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C20 in this effective period.
Related Child Codes
ICD-10-CM does not list child codes under C20 for this display context.
Includes
OfficialICD-10-CM does not list Includes notes for C20 in this effective period.
Excludes 1
Official- malignant carcinoid tumor of the rectum (C7A.026)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for C20 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for C20 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for C20 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is C20 an HCC code?
Yes. C20 maps to Colorectal, Bladder, 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 C20
For C20to 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 C20 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
C20 is the ICD-10-CM diagnosis code for malignant neoplasm of rectum. Cancer that develops in the rectum, which is the final section of the large intestine that connects to the anus. C20 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, C20 maps to Colorectal, Bladder, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, C20 mapped to the same category but with a base RAF weight of 0.306, 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.
Rectal cancer is distinct from colon cancer and has different treatment protocols; ensure correct anatomical coding. Because C20 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 C20 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 the rectum is one of the most common colorectal cancers and has a distinct treatment paradigm from colon cancer, often requiring neoadjuvant chemoradiation followed by total mesorectal excision. Rectal cancer management is complex due to the confined pelvic space, proximity to the anal sphincter complex, and the goal of sphincter preservation when possible. This distinction from colon cancer is critical for risk adjustment because treatment intensity and healthcare resource utilization are significantly higher.
Documentation Requirements
- ✓Documentation confirming rectal location (typically within 15 cm of anal verge)
- ✓Distance from the anal verge to classify as upper, mid, or lower rectal
- ✓Histological type and grade
- ✓Stage of disease including T-stage (depth of rectal wall invasion), N-stage, and circumferential resection margin
- ✓Whether the patient received neoadjuvant therapy and treatment response
Excludes 1, Do NOT code together
- malignant carcinoid tumor of the rectum (C7A.026)
Commonly Confused Codes
- •C19 — Rectosigmoid junction: if the tumor extends proximally to involve the sigmoid junction, use C19
- •C18.7 — Sigmoid colon: sigmoid is proximal to the rectum; confirm anatomical location
- •C21.0 — Anus, unspecified: the anus is distal to the rectum; very low rectal tumors must be distinguished from anal cancer
- •C21.1 — Anal canal: tumors at or below the dentate line are anal canal, not rectal