2023 ICD-10-CM Diagnosis Code C4A.1

Merkel cell carcinoma of eyelid, including canthus

    2016 2017 2018 2019 2020 2021 2022 2023 Non-Billable/Non-Specific Code
  • C4A.1 should not be used for reimbursement purposes as there are multiple codes below it that contain a greater level of detail.
  • The 2023 edition of ICD-10-CM C4A.1 became effective on October 1, 2022.
  • This is the American ICD-10-CM version of C4A.1 - other international versions of ICD-10 C4A.1 may differ.
The following code(s) above C4A.1 contain annotation back-references
Annotation Back-References
In this context, annotation back-references refer to codes that contain:
  • Applicable To annotations, or
  • Code Also annotations, or
  • Code First annotations, or
  • Excludes1 annotations, or
  • Excludes2 annotations, or
  • Includes annotations, or
  • Note annotations, or
  • Use Additional annotations
that may be applicable to C4A.1:
  • C00-D49
    2023 ICD-10-CM Range C00-D49


    • 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).
Code History
  • 2016 (effective 10/1/2015): New code (first year of non-draft ICD-10-CM)
  • 2017 (effective 10/1/2016): No change
  • 2018 (effective 10/1/2017): No change
  • 2019 (effective 10/1/2018): No change
  • 2020 (effective 10/1/2019): No change
  • 2021 (effective 10/1/2020): No change
  • 2022 (effective 10/1/2021): No change
  • 2023 (effective 10/1/2022): No change

Diagnosis Index entries containing back-references to C4A.1:
  • Carcinoma (malignant) - see also Neoplasm, by site, malignant
    • Merkel cell C4A.9
      ICD-10-CM Diagnosis Code C4A.9

      Merkel cell carcinoma, unspecified

        2016 2017 2018 2019 2020 2021 2022 2023 Billable/Specific Code
      Applicable To
      • Merkel cell carcinoma of unspecified site
      • Merkel cell carcinoma NOS
      • canthus C4A.1-
      • eyelid, including canthus C4A.1-

ICD-10-CM Codes Adjacent To C4A.1
C43.61 Malignant melanoma of right upper limb, including shoulder
C43.62 Malignant melanoma of left upper limb, including shoulder
C43.7 Malignant melanoma of lower limb, including hip
C43.70 Malignant melanoma of unspecified lower limb, including hip
C43.71 Malignant melanoma of right lower limb, including hip
C43.72 Malignant melanoma of left lower limb, including hip
C43.8 Malignant melanoma of overlapping sites of skin
C43.9 Malignant melanoma of skin, unspecified
C4A Merkel cell carcinoma
C4A.0 Merkel cell carcinoma of lip
C4A.1 Merkel cell carcinoma of eyelid, including canthus
C4A.10 Merkel cell carcinoma of unspecified eyelid, including canthus
C4A.11 Merkel cell carcinoma of right eyelid, including canthus
C4A.111 Merkel cell carcinoma of right upper eyelid, including canthus
C4A.112 Merkel cell carcinoma of right lower eyelid, including canthus
C4A.12 Merkel cell carcinoma of left eyelid, including canthus
C4A.121 Merkel cell carcinoma of left upper eyelid, including canthus
C4A.122 Merkel cell carcinoma of left lower eyelid, including canthus
C4A.2 Merkel cell carcinoma of ear and external auricular canal
C4A.20 Merkel cell carcinoma of unspecified ear and external auricular canal
C4A.21 Merkel cell carcinoma of right ear and external auricular canal

Reimbursement claims with a date of service on or after October 1, 2015 require the use of ICD-10-CM codes.