2026 ICD-10-CM Diagnosis Code C78.4Secondary malignant neoplasm of small intestine
ICD-10-CM Codes›C00–D49›C76-C80›C78
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 17
- Chronic Condition
C78.4 is a billable ICD-10-CM diagnosis code for secondary malignant neoplasm of small intestine. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 374 through 376. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 21 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Secondary malignancies.
For Medicare Advantage risk adjustment, C78.4 maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic) under the V28 model, adding a risk factor of about 4.209 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C78.4 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adenocarcinoma of Meckel diverticulum
- Adenocarcinoma of small intestine
- Malignant neoplasm of ileum
- Malignant neoplasm of jejunum
- Malignant neoplasm of Meckel's diverticulum
- Metastatic adenocarcinoma to Meckel diverticulum
- Metastatic carcinoma to duodenum
- Metastatic malignant neoplasm to duodenum
- Metastatic malignant neoplasm to ileum
- Metastatic malignant neoplasm to jejunum
- Metastatic malignant neoplasm to Meckel's diverticulum
- Metastatic malignant neoplasm to small intestine
- Metastatic squamous cell carcinoma to small intestine
- Neoplasm of Meckel's diverticulum
- Squamous cell carcinoma of small intestine
- Tumor invades beyond pancreatic capsule to adjacent structures AND/OR organs
- Tumor invades beyond pancreatic capsule to duodenum
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Duodenal Neoplasms
tumors or cancer of the duodenum.Duodenum
the shortest and widest portion of the small intestine adjacent to the pylorus of the stomach. it is named for having the length equal to about the width of 12 fingers.Jejunal Neoplasms
tumors or cancer in the jejunum region of the small intestine (intestine, small).Jejunum
the middle portion of the small intestine, between duodenum and ileum. it represents about 2/5 of the remaining portion of the small intestine below duodenum.
Table of NeoplasmsClinical
Anatomical sites in the Table of Neoplasms that reference this code family.
| Site | Malig. Primary | Malig. Secondary | Ca in situ | Benign | Uncertain | Unspec. |
|---|---|---|---|---|---|---|
| duodenojejunal junction | C17.8 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
| duodenum | C17.0 | C78.4 | D01.49 | D13.2 | D37.2 | D49.0 |
| ileum | C17.2 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
| intestine, intestinal › small | C17.9 | C78.4 | D01.40 | D13.30 | D37.2 | D49.0 |
| intestine, intestinal › small › duodenum | C17.0 | C78.4 | D01.49 | D13.2 | D37.2 | D49.0 |
| intestine, intestinal › small › ileum | C17.2 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
| intestine, intestinal › small › jejunum | C17.1 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
| jejunum | C17.1 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
| Meckel diverticulum, malignant | C17.3 | C78.4 | D01.49 | D13.39 | D37.2 | D49.0 |
Patient EducationClinical
Intestinal Cancer
Your small intestine is part of your digestive system. It is a long tube that connects your stomach to your large intestine. Intestinal cancer is rare, but eating a high-fat diet or having Crohn's disease, celiac disease, or a history of colonic polyps can increase your risk.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C78.4 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C78.4Overview
What is the ICD-10 code for secondary malignant neoplasm of small intestine?
The ICD-10-CM code for secondary malignant neoplasm of small intestine is C78.4 (sometimes written as C784). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is C78.4 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report secondary malignant neoplasm of small intestine on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C78.4 group to?
When secondary malignant neoplasm of small intestine is the principal diagnosis on an inpatient stay, it groups to MS-DRG 374, 375, 376, with relative weights from 0.9243 to 2.1387 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C78.4 a CC or MCC?
CMS lists C78.4 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 21 closely related codes in its exclusion list.
What is the ICD-9 equivalent of C78.4?
Under the General Equivalence Mappings, secondary malignant neoplasm of small intestine converts to ICD-9-CM 197.4 (sec malig neo sm bowel). The mapping is a direct match.
What HCC is C78.4?
C78.4 (secondary malignant neoplasm of small intestine) maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic), commonly written as HCC 17, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 8 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 20.
Does C78.4 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C78.4 adds a risk adjustment factor of about 4.209 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 1.952 to 4.235 depending on the payment segment). HCC 17 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 17 category page.
