Neoplasm of uncertain behavior of histiocytic and mast cells

This code signifies a neoplastic proliferation of histiocytes or mast cells where the biological behavior (benign vs. malignant) cannot be definitively determined from the pathology. These are atypical cellular growths that exhibit some features of malignancy but lack sufficient evidence for a definitive cancer diagnosis.

Assign this code when pathology reports describe a histiocytic or mast cell lesion as "atypical," "of uncertain malignant potential," or "indeterminate." This is appropriate for conditions like atypical mastocytosis or histiocytic lesions that don't meet criteria for a specific malignant lymphoma or leukemia. Documentation must clearly state the uncertain nature of the neoplasm.

• Do not use for clearly benign or clearly malignant histiocytic/mast cell neoplasms; those have specific codes.
• Ensure the pathology report explicitly states "uncertain behavior" or similar terminology.
• Consider sequencing this code as the primary diagnosis if it is the reason for the encounter, followed by any associated symptoms.