Discussion
Syntaxin-1 and INSM1 are sensitive and specific markers of breast tumors with neuroendocrine features, outperforming chromogranin A and CD56. We recommend syntaxin-1 and INSM1 to be included in the routine neuroendocrine immunohistochemical panel.
Methods
Hypercellular (Type B) mucinous carcinomas, solid papillary carcinomas, invasive carcinomas of no special type with neuroendocrine features and ductal carcinomas in situ of neuroendocrine subtype were included in our study. The immunohistochemical panel included chromogranin A, synaptophysin, CD56, syntaxin-1 and INSM1. The specificity of syntaxin-1 and INSM1 was determined using samples negative for chromogranin A, synaptophysin and CD56.
Results
The sensitivity of syntaxin-1 was 84.7% (50/59), with diffuse positivity in more than 60% of the cases. Syntaxin-1 also had an excellent specificity (98.1%). Depending on the definition for positivity, the sensitivity of INSM1 was 89.8% (53/59) or 86.4% (51/59), its specificity being 57.4% or 88.9%. The sensitivities of chromogranin A, synaptophysin and CD56 were 98.3, 74.6 and 22.4%, respectively.