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C20 ICD-10-CM Code: Malignant neoplasm of rectum

C20 maps to CMS-HCC V28 22. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC20

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of digestive organs (C15-C26)

C20

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of rectum

Cancer that develops in the rectum, which is the final section of the large intestine that connects to the anus.

Buddy the Bee presenting code insight

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.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 22

Coefficient HCC 22: 0.363 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 011

Code-level coefficient reference

ESRD/PACE

HCC 11

Code-level coefficient reference

RXHCC

N/A

—

Not mapped

Code Book Path

Official
C2Malignant neoplasms of digestive organs (C15-C26)C20Malignant neoplasm of rectum

Inclusion Terms

Official
  • Malignant neoplasm of rectal ampulla

Excludes 2

Official
  • gastrointestinal stromal tumors (C49.A-)Inherited from C15-C26

Related Codes

Official

No related codes are included in this display for C20. Check the Code Book for the complete code path.

Includes

Official

No Includes notes are included in this display for C20. Check the code and parent instructions in the Code Book.

Excludes 1

Official
  • malignant carcinoid tumor of the rectum (C7A.026)
  • Kaposi's sarcoma of gastrointestinal sites (C46.4)Inherited from C15-C26

Code First

Official

No Code First sequencing instructions are included in this display for C20. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C20. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C20. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
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

MEAT Support

HCC Buddy guidance
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

Audit Caution

HCC Buddy guidance
Coding anal canal cancer as rectal cancer — the treatment approaches are fundamentally different (chemoradiation for anal, surgery for rectal)
Using C18.9 (colon, unspecified) when the tumor is clearly rectal — the rectum is not the colon
Not recognizing that very low rectal tumors may extend into the anal canal, requiring C21.8 (overlapping sites)
Failing to distinguish between active rectal cancer and personal history of rectal cancer (Z85.048)

Common Mistakes

HCC Buddy guidance
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

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C20 an HCC code?

Yes. C20 (Malignant neoplasm of rectum) maps to HCC 22, Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.363. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C20 is billable and maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C20
Description
Malignant neoplasm of rectum
HCC (V28)
HCC 22 — Bladder, Colorectal, and Other Cancers
RAF reference coefficient
0.363
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers
0.363
ESRDHCC 11, Colorectal/Bladder/and Other Cancers
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C20 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C20

For C20, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • 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

Coder workflow notes

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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 Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Rectal cancer is distinct from colon cancer and has different treatment protocols; ensure correct anatomical coding. For C20, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, 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

  • •Rectal cancer is distinct from colon cancer and has different treatment protocols; ensure correct anatomical coding
  • •Verify the tumor is in the rectum and not in the rectosigmoid junction (C19) or anal canal (C21)

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

Code Hierarchy

└C20Malignant neoplasm of rectum
└C20Malignant neoplasm of rectum

For C20, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

C20 maps to CMS-HCC V28 category 22, Bladder, Colorectal, and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C20. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work C20 in HCC Buddy

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