MKI67 and neuroendocrine neoplasm: Ferrata et al. investigated 22 samples of neuroendocrine neoplasms with a high proliferation index (Ki-67 > 20%) and characterized the intratumoral infiltration of CD3+ and CD8+ T cells by progressive classification: 0 (no staining), 1+ (weak staining), 2+ (moderate staining) and 3+ (strong staining) [21].