What is ICD-10 code C49.A5?

C49.A5 is the ICD-10-CM diagnosis code for Gastrointestinal stromal tumor of rectum. A gastrointestinal stromal tumor that occurs in the rectum, the final segment of the large intestine before the anus. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C49.A5 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C49.A5 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C49.A5 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C49.A5 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C49.A5 map to under V28?

C49.A5 maps to CMS-HCC V28 HCC 23 (Prostate, Breast, and Other Cancers and Tumors). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C49.A5: Gastrointestinal stromal

C49.A5 maps to CMS-HCC V28 23. 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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Code lookupC49.A5

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of mesothelial and soft tissue (C45-C49)

C49.A5

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

Gastrointestinal stromal tumor of rectum

A gastrointestinal stromal tumor that occurs in the rectum, the final segment of the large intestine before the anus.

Buddy Insight

Gastrointestinal stromal tumor of the rectum is an uncommon GIST location (approximately 5% of cases) with unique surgical considerations.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 23

Prostate, Breast, and Other C...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 010

HHS-HCC 010 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 20

Lung, Kidney, and Other Cance...

Code-level coefficient reference

Code Book Path

Official

C49Malignant neoplasm of other connective and soft tissue C49.AGastrointestinal stromal tumor C49.A5Gastrointestinal stromal tumor of rectum

Inclusion Terms

Official

No inclusion terms are included in this display for C49.A5. Check the code and parent instructions in the Code Book.

Excludes 2

Official

Kaposi's sarcoma of soft tissue (C46.1)Inherited from C49
malignant neoplasm of heart (C38.0)Inherited from C49
malignant neoplasm of peripheral nerves and autonomic nervous system (C47.-)Inherited from C49
malignant neoplasm of peritoneum (C48.2)Inherited from C49
malignant neoplasm of retroperitoneum (C48.0)Inherited from C49
malignant neoplasm of uterine ligament (C57.3)Inherited from C49
mesothelioma (C45.-)Inherited from C49

Related Codes

Official

C49.A0Gastrointestinal stromal tumor, unspecified site C49.A1Gastrointestinal stromal tumor of esophagus C49.A2Gastrointestinal stromal tumor of stomach C49.A3Gastrointestinal stromal tumor of small intestine C49.A4Gastrointestinal stromal tumor of large intestine

Includes

Official

malignant neoplasm of blood vesselInherited from C49
malignant neoplasm of bursaInherited from C49
malignant neoplasm of cartilageInherited from C49
malignant neoplasm of fasciaInherited from C49
malignant neoplasm of fatInherited from C49
malignant neoplasm of ligament, except uterineInherited from C49
malignant neoplasm of lymphatic vesselInherited from C49
malignant neoplasm of muscleInherited from C49
malignant neoplasm of synoviaInherited from C49
malignant neoplasm of tendon (sheath)Inherited from C49

Excludes 1

Official

malignant neoplasm of cartilage (of):Inherited from C49
articular (C40-C41)Inherited from C49
larynx (C32.3)Inherited from C49
nose (C30.0)Inherited from C49
malignant neoplasm of connective tissue of breast (C50.-)Inherited from C49

Code First

Official

No Code First sequencing instructions are included in this display for C49.A5. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C49.A5. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C49.A5. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirming rectal GIST with immunohistochemistry

Tumor location relative to the anal verge and sphincter complex

Tumor size and mitotic rate

Endorectal ultrasound or MRI findings showing relationship to rectal wall layers

MEAT Support

HCC Buddy guidance

Pathology confirming rectal GIST with immunohistochemistry

Tumor location relative to the anal verge and sphincter complex

Tumor size and mitotic rate

Endorectal ultrasound or MRI findings showing relationship to rectal wall layers

Audit Caution

HCC Buddy guidance

Confusing rectal GIST with rectal adenocarcinoma — fundamentally different tumors requiring different treatment

Coding a low rectal GIST as an anal canal tumor or vice versa — precise anatomical classification matters

Using the generic rectum cancer code (C20) instead of the GIST-specific code

Not recognizing that rectal GISTs may benefit from neoadjuvant imatinib before surgery

Common Mistakes

HCC Buddy guidance

C20 (Malignant neoplasm of rectum) — rectal adenocarcinoma, not GIST

C49.A4 (GIST of large intestine) — colonic GIST, not rectal

C49.A0 (GIST, unspecified site) — use C49.A5 when rectum is documented

C21._ (Malignant neoplasm of anus) — anal canal malignancy, not rectal GIST

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 C49.A5 an HCC code?

Yes. C49.A5 (Gastrointestinal stromal tumor of rectum) maps to HCC 23, Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.186. 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: C49.A5 is billable and maps to V28 HCC 23, Prostate, Breast, and Other Cancers and Tumors. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C49.A5
Description: Gastrointestinal stromal tumor of rectum
HCC (V28): HCC 23 — Prostate, Breast, and Other Cancers and Tumors
RAF reference coefficient: 0.186
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors

0.186

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 20, Lung, Kidney, and Other Cancers; Secondary Cancer of Lymph Nodes and Other Sites

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 C49.A5 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C49.A5

For C49.A5, 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

C49.A5 is the ICD-10-CM diagnosis code for gastrointestinal stromal tumor of rectum. A gastrointestinal stromal tumor that occurs in the rectum, the final segment of the large intestine before the anus. C49.A5 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of mesothelial and soft tissue (c45-c49).

Under the CMS-HCC V28 risk adjustment model, C49.A5 maps to Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a source-labeled community, non-dual, aged reference coefficient of 0.186. No V24 mapping is shown for C49.A5; 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.

Verify the tumor is in the rectum and not in the sigmoid colon or anal canal. For C49.A5, 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 C49.A5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify the tumor is in the rectum and not in the sigmoid colon or anal canal
•Note any involvement of surrounding structures for staging and treatment planning documentation

Clinical Significance

Gastrointestinal stromal tumor of the rectum is an uncommon GIST location (approximately 5% of cases) with unique surgical considerations. Rectal GISTs often require neoadjuvant imatinib to shrink the tumor and enable sphincter-preserving surgery, making accurate diagnosis and coding critical for treatment authorization.

Documentation Requirements

✓Pathology confirming rectal GIST with immunohistochemistry
✓Tumor location relative to the anal verge and sphincter complex
✓Tumor size and mitotic rate
✓Endorectal ultrasound or MRI findings showing relationship to rectal wall layers
✓Treatment plan including neoadjuvant therapy consideration