C44.521 vs C50.911

C44.521 (Squamous cell carcinoma of skin of breast) compared with C50.911 (Malignant neoplasm of unspecified site of right female breast), from the official CMS tabular data.

Summary

These codes should not be reported together because C50.911’s tabular entry lists C44.521 under Excludes1.

Official rule

What is different?

The conditions named.C44.521 is “Squamous cell carcinoma of skin of breast”; C50.911 is “Malignant neoplasm of unspecified site of right female breast”.

Registry fact

Can these codes be reported together?

No.C50.911’s entry carries an Excludes1 note covering C44.521: “skin of breast (C44.501, C44.511, C44.521, C44.591)”. Both may be reported only when the documentation shows the two conditions are unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

Yes.C50.911’s tabular entry: “skin of breast (C44.501, C44.511, C44.521, C44.591)”. The note covers C44.521.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes2 relationship?

None.Neither entry carries an Excludes2 note that names the other code.

Official rule

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?

No.Both are billable codes, and neither contains the other.

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?

Conflict

Excludes1 conflict

C50.911

Malignant neoplasm of unspecified site of right female breast

↔

C44.521

Squamous cell carcinoma of skin of breast

What we found

No — do not report together.C50.911 carries an Excludes1 note covering C44.521: “skin of breast (C44.501, C44.511, C44.521, C44.591)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

What to review

Report one of the two. Both may be reported only when the documentation shows the two conditions are unrelated to each other.

Guide: Excludes1 vs Excludes2 Check these on a claim

Why it matters

An Excludes1 note means the two conditions cannot occur together, so the pair should not be reported for the same encounter. The sole exception is when the conditions are documented as unrelated to each other.

Source / rule

CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a

Official guidance behind these answers

Section I.A.12.a — Excludes1 · applies to: Excludes1
A type 1 Excludes note is a pure excludes note. It means “NOT CODED HERE!” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition. An exception to the Excludes1 definition is the circumstance when the two conditions are unrelated to each other. If it is not clear whether the two conditions involving an Excludes1 note are related or not, query the provider. For example, code F45.8, Other somatoform disorders, has an Excludes1 note for "sleep related teeth grinding (G47.63)," because "teeth grinding" is an inclusion term under F45.8. Only one of these two codes should be assigned for teeth grinding. However psychogenic dysmenorrhea is also an inclusion term under F45.8, and a patient could have both this condition and sleep related teeth grinding. In this case, the two conditions are clearly unrelated to each other, and so it would be appropriate to report F45.8 and G47.63 together.
ICD-10-CM Official Guidelines FY2026

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

	C44.521Squamous cell carcinoma of skin of breast	C50.911Malignant neoplasm of unspecified site of right female breast
Billing status	Billable	Billable
Classification	C00-D49 — Neoplasms (C00-D49)	C00-D49 — Neoplasms (C00-D49)
Definition	Squamous cell carcinoma of skin of breast is a billable ICD-10-CM diagnosis code (C44.521).	Malignant neoplasm of unspecified site of right female breast is a billable ICD-10-CM diagnosis code (C50.911).
Includes	malignant neoplasm of sebaceous glands malignant neoplasm of sweat glands	connective tissue of breast Paget's disease of breast Paget's disease of nipple
Excludes1	anus NOS (C21.0) scrotum (C63.2) Kaposi's sarcoma of skin (C46.0) malignant melanoma of skin (C43.-) malignant neoplasm of skin of genital organs (C51-C52, C60.-, C63.2) Merkel cell carcinoma (C4A.-)	skin of breast (C44.501, C44.511, C44.521, C44.591)
Use additional code	—	code to identify estrogen, and other hormones and factors receptor status (Z17.-)

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.

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Derived from the official CMS ICD-10-CM tabular data (FY2026). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources