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C4A vs C7A.091

C4A (Merkel cell carcinoma) compared with C7A.091 (Malignant carcinoid tumor of the thymus), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes can be reported together when both conditions are documented, because C7A.091 lists C4A under Excludes2, which marks them as distinct conditions.

Official rule
What is different?

The conditions named and billing status.C4A is “Merkel cell carcinoma”; C7A.091 is “Malignant carcinoid tumor of the thymus”. C4A is a non-billable header; C7A.091 is billable.

Registry fact

Can these codes be reported together?

Yes, when both are documented.C7A.091 lists C4A under Excludes2: “Merkel cell carcinoma (C4A.-)”. Excludes2 marks distinct conditions that may both be reported when both are documented.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

None.Neither entry carries an Excludes1 note that names the other code.

Official rule

Is there an Excludes2 relationship?

Yes.C7A.091’s tabular entry: “Merkel cell carcinoma (C4A.-)”. The note covers C4A.

Official ruleGuide: Excludes1 vs Excludes2

Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Is one a parent or header code?

One is a header.C4A is a non-billable header, but C7A.091 is not one of its subdivisions.

Registry fact

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Informational

Excludes2 relationship

C7A.091
Malignant carcinoid tumor of the thymus
↔
C4A
Merkel cell carcinoma

What we found

Yes, when both are documented.C7A.091 carries an Excludes2 note covering C4A: “Merkel cell carcinoma (C4A.-)”

Excludes2 marks distinct conditions — both may be reported when both are documented.

What to review

Report both only when the documentation supports both conditions; otherwise report the one documented.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes2 note means the excluded condition is not part of the code above it, but a patient can have both. Report both when both are documented.

Source / rule

CMS ICD-10-CM tabular instructional notes

Official guidance behind these answers

  • Section I.A.12.b — Excludes2 · applies to: Excludes2

    A type 2 Excludes note represents “Not included here.” An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
C4A

Merkel cell carcinoma

C7A.091

Malignant carcinoid tumor of the thymus

StatusDiffers
C4A
Non-billable header

A header is not reported on a claim; a code beneath it is.

Report instead: C4A.0, C4A.10, C4A.111, C4A.112, C4A.121

C7A.091
Billable
Excludes2Differs
C4A

None at this code

C7A.091
  • malignant pancreatic islet cell tumors (C25.4)
  • Merkel cell carcinoma (C4A.-)
Use additional codeDiffers
C4A

None at this code

C7A.091
  • code to identify any associated endocrine syndrome, such as:
  • carcinoid syndrome (E34.00)
Code alsoDiffers
C4A

None at this code

C7A.091
  • any associated multiple endocrine neoplasia [MEN] syndromes (E31.2-)
CategoryDiffers
C4A

Is itself a category

C7A.091

C7A Malignant neuroendocrine tumors

ChapterSame for both

C00-D49 — Neoplasms (C00-D49)

No Excludes1, Code first, Includes and 7th character note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, notes every code shares are dimmed.

Edit this comparisonCheck a whole claim

Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources