This case contributes to the growing evidence of HER2 in the pathogenesis of metastatic extramammary Paget's disease and emphasizes the importance of repetitive, genomic analysis in rare diseases.
To assess the optimal methods for detection of HER2-positive EMPD, 73 EMPD samples were analyzed by immunohistochemical (IHC) staining, fluorescence in situ hybridization (FISH), and the HER2 testing algorithm for breast cancer of the American Society of Clinical Oncology/College of American Pathologists, which combined the results of IHC staining and FISH.
Among the 10 cases of EMPD without invasion, seven showed a luminal A profile and three showed a luminal B profile (all HER2-amplified); no HER2-enriched or basal-like subtypes were identified.
These results suggest that patients with EMPD strongly positive for HER-2 may have high risk for lymph node metastasis and should be followed up carefully.
However, the higher incidence of HER2 gain and the relatively lower incidence of aberrant TUBB3 expression suggested that HER2-targeted immunotherapy combined with taxane derivatives is warranted for metastatic EMPD, and that HER2 and TUBB3 status might be a good biomarker for determining the most appropriate therapeutic modality.
These results suggest the contribution of the HER2 signaling pathway to the pathogenesis and progression of some cases of extramammary Paget's disease, for which clinical use of molecular target therapy against the HER2 pathway is warranted.
Although we previously showed that erbB-2 overexpression may play a part in the progression of EMPD, molecular genetic defects underlying the development of EMPD are poorly understood.
Frequent overexpression of erbB-2 by either gene amplification or possible transcriptional activation in invasive primary tumors and metastases suggests an important part for this oncogene in the progression of extramammary Paget's disease.
Sections of formalin-fixed, paraffin-embedded tumour tissue from 22 patients with mammary and extramammary Paget's disease have been stained immunohistochemically using a monoclonal antibody (NCL-CB11) raised against a synthetic peptide from the C-terminal end of the predicted sequence of the c-erbB-2 protein product.
Serum levels of carcinoembryonic antigen (CEA) and cytokeratin 19 fragment (CYFRA) are not elevated in most patients with extramammary Paget disease (EMPD) without metastasis.
Serum carcinoembryonic antigen (CEA) and cytokeratin 19 fragment 21-1 (CYFRA 21-1) levels have been identified as candidate biomarkers for tumour progression in EMPD.
Our study shows that the concordant overexpression of p53 and p73 and the decreased expression of p63 may play a pivotal role in the pathogenesis of EMPD.
Since expression of p53 mRNA and p53 protein was not high in any of the 3 EMPD samples compared to the intact skin of the same patient, we analyzed PIG7/LITAF cDNA mutations among 12 EMPD samples (including the former 4) by PCR-SSCP.
Our previous study in extramammary Paget's disease showed neither p53 mutations nor allelic loss at selected loci implicated in other cancers, suggesting a pathogenesis of this skin cancer different from other common epithelial malignancies.