ICD-10 Code for Merkel Cell Carcinoma
The ICD-10 code for Merkel cell carcinoma is C4A, with the fourth character specifying the anatomic location of the tumor.
Complete ICD-10 Coding Structure
The specific codes are organized by anatomic site:
- C4A.0 - Merkel cell carcinoma of lip
- C4A.1 - Merkel cell carcinoma of eyelid, including canthus (with fifth character for laterality: 0=unspecified, 1=right, 2=left)
- C4A.2 - Merkel cell carcinoma of ear and external auricular canal (with fifth character for laterality)
- 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 (includes anal margin, anal skin, perianal skin, skin of breast)
- C4A.6 - Merkel cell carcinoma of upper limb, including shoulder (with fifth character for laterality)
- C4A.7 - Merkel cell carcinoma of lower limb, including hip (with fifth character for laterality)
- C4A.8 - Merkel cell carcinoma of overlapping sites
- C4A.9 - Merkel cell carcinoma, unspecified
Clinical Context
Merkel cell carcinoma is a rare, aggressive neuroendocrine skin tumor that most commonly occurs in sun-exposed areas, particularly the head and neck region and extremities in elderly patients 1, 2. The tumor is characterized by high rates of lymph node metastases (50%) and local recurrences (25-77%), with 5-year survival rates ranging from 30-74% depending on stage 1.
Important Coding Considerations
When coding for Merkel cell carcinoma, specify the exact anatomic location to the highest level of detail possible, as this impacts staging and treatment planning 3, 4. The head and neck region requires particular attention due to complex lymphatic drainage patterns and higher risk of false-negative sentinel lymph node biopsies 5, 6.