C4A
Merkel cell carcinoma
Not billable — category only FY2026 2025-10-01 → 2026-09-30
Instructional notes 8
C00-D49chapter
Notes
- 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).C25.9
Index entries leading here filed at null
No alphabetic index entry points at this code.
Subordinate codes 10
C4A.0 Merkel cell carcinoma of lip C4A.1 Merkel cell carcinoma of eyelid, including canthus C4A.2 Merkel cell carcinoma of ear and external auricular canal C4A.3 Merkel cell carcinoma of other and unspecified parts of face C4A.4 Merkel cell carcinoma of scalp and neck C4A.5 Merkel cell carcinoma of trunk C4A.6 Merkel cell carcinoma of upper limb, including shoulder C4A.7 Merkel cell carcinoma of lower limb, including hip C4A.8 Merkel cell carcinoma of overlapping sites C4A.9 Merkel cell carcinoma, unspecified
Medications 5
7 Carcinoma, Merkel Cell drugs 32 Carcinoma, Renal Cell drugs 20 Carcinoma, Squamous Cell drugs 7 Carcinoma, Transitional Cell drugs 4 Carcinoma, Small Cell drugs
MED-RT files conditions by MeSH, which carves the world differently from ICD-10. These are name matches on this code's description, offered as candidates — not as an assertion that they are this code.
Additional references
AHA Coding Clinic® Licence required
Official coding advice for this code. Published by the American Hospital Association. Not included in this installation.