Malignant poorly differentiated neuroendocrine tumors

This code signifies a highly aggressive form of neuroendocrine neoplasm characterized by rapid growth and poor cellular differentiation. These tumors originate from neuroendocrine cells throughout the body, often presenting with widespread metastatic disease at diagnosis due to their aggressive nature.

Apply this code when documentation explicitly states a diagnosis of a malignant neuroendocrine tumor with "poorly differentiated" features. This typically includes high-grade neuroendocrine carcinomas (NECs) as opposed to well-differentiated neuroendocrine tumors (NETs). Pathological reports confirming high mitotic activity, necrosis, and a high Ki-67 index are crucial for supporting this diagnosis.

• Distinguish carefully between "poorly differentiated" and "well-differentiated" neuroendocrine tumors; the latter are coded elsewhere.
• Always review the pathology report for definitive differentiation status and grade.
• Do not use this code for carcinoid tumors, which are generally well-differentiated NETs.