MKI67 and carcinoma: NECs are divided into three main categories based on the malignancy potential of the carcinoma [6]: well-differentiated endocrine carcinoma (<2 cm in size and Ki-67 index of <2%, well-differentiated endocrine carcinoma (>2 cm in size, Ki-67 index of >2%, or presence of angioinvasion), and poorly differentiated endocrine carcinoma (Ki-67 index of >20%).