atypical pulmonary carcinoid tumour atypical pulmonary carcinoid tumour atypical pulmonary carcinoid tumour is a subtype of pulmonary carcinoid tumor. it is an uncommon low-grade malignant lung mass that is most often in the central airways of the lung. it is also known as "atypical lung carcinoid tumour", " atypical lung carcinoid" or "moderately differentiated neuroendocrine carcinoma". atypical pulmonary carcinoid tumouratypical pulmonary carcinoid. h&e stain.specialtyoncology it is a more aggressive than typical carcinoid tumors: nodal metastases in 70% vs. 5%. the 5 year survival is 49-69%. atypical carcinoid tumors have increased mitotic activity (2-10 per 10 hpf), nuclear pleomorphism or foci of necrosis. morphological differential diagnosis atypical carcinoid of the lung exhibiting endobronchial growth, increased mitotic activity was seen (2-10 per 10 hpf). h&e stain. typical pulmonary carcinoid tumor typical pulmonary carcinoid lacks comedo-like necrosis, and has < 0.2 mitotic figures/hpf.