Using the mitosis-specific marker anti-phosphohistone H3 to assess mitosis in pulmonary neuroendocrine carcinomas

Counting mitotic figures (MFs) is one of the essential factors for determining the histologic grade of pulmonary neuroendocrine carcinoma (NEC). We analyzed MFs by using a mitotic-specific antibody of phosphohistone H3 (PHH3) in 113 lung NECs (66 typical carcinoids [TCs], 12 atypical carcinoids [ACs], 20 large cell NECs [LCNECs], and 15 small cell lung carcinomas [SCLCs]). Subdivided by histologic subtype, the mean PHH3-stained MFs (mPHMFs) were 0.09 per high-power field (hpf) in TCs, 0.39/hpf in ACs, 7.84/hpf in LCNECs, and 9.42 in SCLCs. From the 5-year overall survival rate for mPHMFs, an mPHMF of more than 1.0 was the best threshold in all NECs and an mPHMF of more than 0.4 was the best threshold for differentiating ACs from TCs. These values correspond to 4/10 hpf and 10/10 hpf. We showed that the PHH3-based mitosis-counting method is a reliable, easy method for counting mitoses in pulmonary NECs.