KRT5 and small cell carcinoma: The napsin A positive case was TTF-1/CD56/synaptophysin (diffuse and strong) positive; chromogranin A was focal and weak; p63 and CK5/6 were negative; Ki67 proliferation index was 90%, and the napsin staining was described as "very rare cells showing cytoplasmic staining with napsin A." All TTF-1-negative small cell carcinomas with reported napsin A staining were napsin A negative (0/3) (Table 1).