C43 vs C4A

C43 (Malignant melanoma of skin) compared with C4A (Merkel cell carcinoma), from the official CMS tabular data. Both may be reported when both conditions are documented (Excludes2).

Can these codes be reported together?

Yes, when both are documented. C43 carries an Excludes2 note covering C4A: “Merkel cell carcinoma (C4A.-)”

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

Side by side

	C43Malignant melanoma of skin	C4AMerkel cell carcinoma
Billing status	Non-billable header Report instead: C43.0, C43.10, C43.111, C43.112, C43.121	Non-billable header Report instead: C4A.0, C4A.10, C4A.111, C4A.112, C4A.121
Classification	C00-D49 — Neoplasms (C00-D49)	C00-D49 — Neoplasms (C00-D49)
Definition	Malignant melanoma of skin is a non-billable ICD-10-CM category code (C43).	Merkel cell carcinoma is a non-billable ICD-10-CM category code (C4A).

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Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources