What is ICD-10 code C7A.1?

C7A.1 is the ICD-10-CM diagnosis code for Malignant poorly differentiated neuroendocrine tumors. A rare, aggressive cancer of hormone-producing cells that appear abnormal under the microscope and do not have well-defined characteristics. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C7A.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C7A.1 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. C7A.1 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. C7A.1 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 C7A.1 map to under V28?

C7A.1 maps to CMS-HCC V28 HCC 21 (Lymphoma and Other Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C7A.1: Malignant poorly

C7A.1 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools

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Code lookupC7A.1

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neuroendocrine tumors (C7A)

C7A.1

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

Malignant poorly differentiated neuroendocrine tumors

A rare, aggressive cancer of hormone-producing cells that appear abnormal under the microscope and do not have well-defined characteristics.

Buddy Insight

Malignant poorly differentiated neuroendocrine tumors represent high-grade, aggressive neuroendocrine carcinomas with poor cellular differentiation on pathology.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

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 012

HHS-HCC 012 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 12

Breast/Prostate/and Other Can...

Code-level coefficient reference

RXHCC

Mapped

HCC 22

Prostate, Breast, Bladder, an...

Code-level coefficient reference

Code Book Path

Official

C7AMalignant neuroendocrine tumors C7A.1Malignant poorly differentiated neuroendocrine tumors

Inclusion Terms

Official

Malignant poorly differentiated neuroendocrine tumor NOS
Malignant poorly differentiated neuroendocrine carcinoma, any site
High grade neuroendocrine carcinoma, any site

Excludes 2

Official

malignant pancreatic islet cell tumors (C25.4)Inherited from C7A
Merkel cell carcinoma (C4A.-)Inherited from C7A

Related Codes

Official

C7A.0Malignant carcinoid tumors C7A.8Other malignant neuroendocrine tumors

Includes

Official

No Includes notes are included in this display for C7A.1. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C7A.1. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C7A.1. Check the code and parent instructions in the Code Book.

Use Additional

Official

code to identify any associated endocrine syndrome, such as:Inherited from C7A
carcinoid syndrome (E34.00)Inherited from C7A

Code Also

Official

any associated multiple endocrine neoplasia [MEN] syndromes (E31.2-)Inherited from C7A

Buddy Documentation Tip

HCC Buddy guidance

Pathology report confirming poorly differentiated/high-grade neuroendocrine histology (Grade 3)

Ki-67 proliferation index (typically greater than 20%)

Primary site of origin if known (code the primary site separately)

Small cell versus large cell neuroendocrine carcinoma distinction

MEAT Support

HCC Buddy guidance

Pathology report confirming poorly differentiated/high-grade neuroendocrine histology (Grade 3)

Ki-67 proliferation index (typically greater than 20%)

Primary site of origin if known (code the primary site separately)

Small cell versus large cell neuroendocrine carcinoma distinction

Audit Caution

HCC Buddy guidance

Coding poorly differentiated neuroendocrine carcinomas as carcinoid tumors (C7A.0 series) — differentiation grade is the critical distinction

Missing the Ki-67 index in pathology review, which is essential for grading neuroendocrine tumors

Not coding the primary site separately when it is identified — C7A.1 focuses on differentiation level, not location

Confusing with small cell lung cancer when the primary is pulmonary — SCLC has its own coding pathway

Common Mistakes

HCC Buddy guidance

C7A.0 series — Site-specific malignant carcinoid tumors: Carcinoids are typically well-differentiated (G1-G2); C7A.1 is for poorly differentiated (G3) neuroendocrine tumors

C34.90 — Malignant neoplasm of bronchus/lung: Small cell lung cancer is a form of poorly differentiated neuroendocrine carcinoma but has its own specific code

C7A.8 — Other malignant neuroendocrine tumors: Use C7A.8 for neuroendocrine tumors that don't fit carcinoid or poorly differentiated categories

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 C7A.1 an HCC code?

Yes. C7A.1 (Malignant poorly differentiated neuroendocrine tumors) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. 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: C7A.1 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C7A.1
Description: Malignant poorly differentiated neuroendocrine tumors
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

ESRDHCC 12, Breast/Prostate/and Other Cancers and Tumors

Not separately weighted

RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors

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 C7A.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C7A.1

For C7A.1, 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

C7A.1 is the ICD-10-CM diagnosis code for malignant poorly differentiated neuroendocrine tumors. A rare, aggressive cancer of hormone-producing cells that appear abnormal under the microscope and do not have well-defined characteristics. C7A.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neuroendocrine tumors (c7a).

Under the CMS-HCC V28 risk adjustment model, C7A.1 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C7A.1; 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.

Poorly differentiated neuroendocrine tumors have worse prognosis; ensure pathology confirms poor differentiation grade. For C7A.1, 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 C7A.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Poorly differentiated neuroendocrine tumors have worse prognosis; ensure pathology confirms poor differentiation grade
•Document the primary site separately if known, as this code focuses on differentiation level rather than location

Clinical Significance

Malignant poorly differentiated neuroendocrine tumors represent high-grade, aggressive neuroendocrine carcinomas with poor cellular differentiation on pathology. These tumors behave similarly to small cell carcinoma and carry a significantly worse prognosis than well-differentiated carcinoid tumors. They are typically fast-growing, have high mitotic rates (Ki-67 greater than 20%), and frequently present with advanced or metastatic disease requiring aggressive chemotherapy regimens.

Documentation Requirements

✓Pathology report confirming poorly differentiated/high-grade neuroendocrine histology (Grade 3)
✓Ki-67 proliferation index (typically greater than 20%)
✓Primary site of origin if known (code the primary site separately)
✓Small cell versus large cell neuroendocrine carcinoma distinction
✓Stage at diagnosis including metastatic workup
✓Treatment regimen (typically platinum-based chemotherapy similar to small cell lung cancer)

Commonly Confused Codes

•C7A.0 series: Site-specific malignant carcinoid tumors: Carcinoids are typically well-differentiated (G1-G2); C7A.1 is for poorly differentiated (G3) neuroendocrine tumors
•C34.90: Malignant neoplasm of bronchus/lung: Small cell lung cancer is a form of poorly differentiated neuroendocrine carcinoma but has its own specific code
•C7A.8: Other malignant neuroendocrine tumors: Use C7A.8 for neuroendocrine tumors that don't fit carcinoid or poorly differentiated categories