Merkel cell carcinoma of other part of trunk

This code signifies a rare and aggressive neuroendocrine carcinoma of the skin, specifically Merkel cell carcinoma, located on any part of the trunk other than the chest wall, abdominal wall, or groin. This malignancy typically presents as a rapidly growing, firm, painless nodule. Histopathological confirmation is essential for diagnosis.

Apply this code when documentation clearly identifies Merkel cell carcinoma affecting the back, flank, perineum, or buttocks. This code is appropriate for both primary and recurrent tumors in these trunk locations. Supporting documentation will include pathology reports confirming Merkel cell carcinoma and physician notes specifying the tumor's exact anatomical site on the trunk.

• Differentiate from C4A.1-C4A.4 for Merkel cell carcinoma of specific trunk sites (e.g., C4A.1 for Merkel cell carcinoma of skin of chest wall).
• Ensure the documentation specifies "other part of trunk" or a non-specified trunk location to justify this code.
• Always sequence this code as the primary diagnosis when it is the reason for the encounter, unless another condition is the primary focus of treatment.