Alphabetic Index FY2027

C4A.9

Merkel cell carcinoma, unspecified

FY2027Chapter 2: Neoplasms/C43–C44 Melanoma and other malignant neoplasms of skin

BillableComplete code, valid to report

    C4A.9 (also written C4A9) is a billable ICD-10-CM diagnosis code for merkel cell carcinoma, unspecified. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 24 codes in category C4A (Merkel cell carcinoma). The Alphabetic Index lists it under 1 entry.

    Guidelines tip

    From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.

    A primary malignancy code stays in use until treatment directed at that site is completed. After that, with no evidence of disease at the site, Z85 gives the former site.

    Guidelines I.C.2.mCurrent malignancy versus personal history of malignancyRead the official text

    Inclusion terms

    Conditions classified to this code.

    This code
    • Merkel cell carcinoma of unspecified site
    • Merkel cell carcinoma NOS

    Notes

    Also from chapter/block level (8 notes)
    Inherited from Chapter 2 Neoplasms
    • Functional activity
    • All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
    • Morphology [Histology]
    • Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
    • Primary malignant neoplasms overlapping site boundaries
    • A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
    • Malignant neoplasm of ectopic tissue
    • Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).

    Alphabetic Index terms

    Terms the official Alphabetic Index lists for this code. 1 entry