Diagnosing Xeroderma Pigmentosum Group C by Immunohistochemistry

Abstract

Xeroderma pigmentosum (XP) is a group of rare inherited human neurocutaneous diseases, and the group C (XPC) is the major group of patients with XP in Europe, North America, and South America. Current molecular diagnostic methods for XP require specialized, expensive, and time-consuming UV sensitivity and DNA repair assays followed by gene sequencing. To determine whether immunohistochemistry (IHC) would be a robust alternative method to diagnose patients with XPC, we stained sections of paraffin-embedded skin biopsies for XPC by IHC, using 69 archived blocks from confirmed or clinically suspect patients with XPA, XPC, XPD, XPE, and without XP. We found that XPC expression was strong in all skin biopsies from patients without (14 of 14) and other patients with XP (4 of 4), whereas XPC expression was lost in all biopsies from confirmed XPC patients (29 of 29). Patches of strong XPC signal could be detected in sun-damaged skin, squamous and basal cell carcinomas from patients with XPC that colocalized with strong expression of p53 and Ki-67. Patients with XPC can therefore be diagnosed by IHC from paraffin-embedded skin biopsies from regions of skin that are without sun damage or sun-induced tumors. IHC is therefore a robust alternative method to diagnose patients with XPC. This fast and inexpensive method should increase the options for the diagnosis of patients with XPC from paraffin-embedded skin biopsies and could be developed for other complementation groups.

The DNA Damage-Binding Protein XPC Is a Frequent Target for Inactivation in Squamous Cell Carcinomas

“…If only archival blocks of tumor biopsies were available for a particular XP patient, diagnosis would need to be based on XPC expression in flanking normal skin or lymphocyte infiltrations. 17 Our previous results indicated apparent reappearance of XPC antigenicity in tumor tissue of XP-C patients. 17 We now recognize that this observation may represent crossreaction of the XPC antibody ( Figure 1B) to denaturated p53 that is highly mutated in XP-C patients and may therefore denature more easily.…”

“…17 Our previous results indicated apparent reappearance of XPC antigenicity in tumor tissue of XP-C patients. 17 We now recognize that this observation may represent crossreaction of the XPC antibody ( Figure 1B) to denaturated p53 that is highly mutated in XP-C patients and may therefore denature more easily. 15,33,34 In 99 of 100 samples, plugs of nonmalignant skin showed positive staining for XPC permitting discrimination between tumor-specific loss of XPC in SCCs from non XP-C donors and genetic loss in an XP-C patient.…”

“…The loss of XPC expression must involve inactivation of both alleles of XPC because our IHC does not discriminate obligate XP-C heterozygotes from normal donors. 17 The analysis of XPC expression by immunohistochemistry on a tissue microarray of 221 SCCs from immunocompetent and immunosuppressed patients showed that XPC expression was lost in 26 to 49% …”

“…17 When we examined SCCs from non XP-C patients, we found that some cases showed continued expression of XPC in normal basal keratinocytes adjacent to the tumor but loss of XPC expression in the tumor tissue itself, except focally in rare keratinocytes (Figure 2, B, D, F and H). We examined XPC expression by immunohistochemistry in a tissue microarray of 244 tissue cores, of which a total of 221 could be analyzed (the remainder were lost or degraded and gave no information).…”

“…Cultures of XPCdeficient cells and skin biopsies from XP-C families were previously used for validation of the method, after informed consent. 17 In this previous study we showed that the antibody consistently detected XPC loss in all of the known XP-C patients analyzed and identified several previously undiagnosed patients. XPC immunostaining was performed on 5-m sections of paraffin-embedded tissue using the XPC mouse monoclonal antibody.…”