C78.5 ICD-10-CM Code: Secondary malignant neoplasm of large intestine and rectum
C78.5 maps to CMS-HCC V28 17. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80)
C78.5
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSecondary malignant neoplasm of large intestine and rectum
Cancer that has spread to the large intestine (colon) or rectum from a primary cancer that started in another part of the body.
Buddy Insight
Secondary malignant neoplasm of the large intestine and rectum indicates metastatic disease to the colon or rectum from a cancer that originated elsewhere.
CMS-HCC V28
MappedHCC 17
Coefficient HCC 17: 4.209 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 008
Code-level coefficient reference
ESRD/PACE
MappedHCC 8
Code-level coefficient reference
RXHCC
MappedHCC 20
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C78.5. Check the code and parent instructions in the Code Book.
Excludes 2
Official- lymph node metastases (C77.0)Inherited from C78
Related Codes
Includes
OfficialNo Includes notes are included in this display for C78.5. Check the code and parent instructions in the Code Book.
Excludes 1
Official- secondary carcinoid tumors of liver (C7B.02)Inherited from C78
- secondary carcinoid tumors of peritoneum (C7B.04)Inherited from C78
Code First
OfficialNo Code First sequencing instructions are included in this display for C78.5. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C78.5. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C78.5. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 C78.5 an HCC code?
Yes. C78.5 (Secondary malignant neoplasm of large intestine and rectum) maps to HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 4.209. 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: C78.5 is billable and maps to V28 HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C78.5
- Description
- Secondary malignant neoplasm of large intestine and rectum
- HCC (V28)
- HCC 17 — Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic
- RAF reference coefficient
- 4.209
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C78.5 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C78.5
For C78.5, 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
C78.5 is the ICD-10-CM diagnosis code for secondary malignant neoplasm of large intestine and rectum. Cancer that has spread to the large intestine (colon) or rectum from a primary cancer that started in another part of the body. C78.5 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of ill-defined, other secondary and unspecified sites (c76-c80).
Under the CMS-HCC V28 risk adjustment model, C78.5 maps to Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic (HCC 17) with a source-labeled community, non-dual, aged reference coefficient of 4.209. No V24 mapping is shown for C78.5; use the applicable model and payment year when reviewing the V28 mapping. 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.
Document whether the metastasis is to the colon, rectum, or both; this code encompasses the entire large intestine and rectum. For C78.5, 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 C78.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document whether the metastasis is to the colon, rectum, or both; this code encompasses the entire large intestine and rectum
- •Code the primary malignancy separately and ensure clinical documentation confirms metastatic rather than primary colorectal cancer
Clinical Significance
Secondary malignant neoplasm of the large intestine and rectum indicates metastatic disease to the colon or rectum from a cancer that originated elsewhere. This is an important distinction from primary colorectal cancer, which is far more common. Proper identification of secondary colorectal malignancy affects staging, treatment approach, and prognosis estimation.
Documentation Requirements
- ✓Primary cancer site must be identified and coded separately
- ✓Documentation confirming metastatic rather than primary colorectal cancer — pathology, imaging, or clinical assessment
- ✓Specific segment of large intestine if documented — ascending, transverse, descending, sigmoid, or rectum
- ✓Whether diagnosed by colonoscopy, imaging, or surgical specimen
- ✓Complications such as obstruction, bleeding, or perforation
Commonly Confused Codes
- •C18.0-C18.9: Primary malignant neoplasm of colon; primary colorectal cancer is far more common than metastatic disease to the colon
- •C20: Primary malignant neoplasm of rectum; distinguish from metastatic disease to the rectum
- •C78.4: Secondary malignant neoplasm of small intestine; verify small versus large intestine involvement
- •C78.6: Secondary malignant neoplasm of peritoneum; peritoneal carcinomatosis may involve bowel but is coded separately