Immunohistochemical Detection of Cancer-Testis Antigen PRAME

Abstract

Cancer-testis (CT) antigens were identified by their ability to elicit T- or B-cell immune responses in the autologous host. They are typically expressed in a wide variety of neoplasms and in normal adult tissues are restricted to testicular germ cells. PReferentially expressed Antigen of Melanoma (PRAME) is a member of the family of nonclassical CT antigens being expressed in a few other normal tissues besides testis. Interestingly, knowledge about the protein expression of many CT antigens is still incomplete due to the limited availability of reagents for their immunohistochemical detection. Here, we tested several commercially available serological reagents and identified a monoclonal antibody suitable for the immunohistochemical detection of PRAME in formalin-fixed paraffin-embedded specimens. We also tested a wide array of normal and neoplastic tissues. PRAME protein expression in normal tissues is congruent with original molecular data being present in the testis, and at low levels in the endometrium, adrenal cortex, and adult as well as fetal ovary. In tumors, there is diffuse PRAME immunoreactivity in most metastatic melanomas, myxoid liposarcomas, and synovial sarcomas. Other neoplasms such as seminomas and carcinomas of various origins including endometrial, serous ovarian, mammary ductal, lung, and renal showed an intermediate proportion of cases and variable extent of tumor cells positive for PRAME protein expression. As seen with other CT antigens, hepatocellular and colorectal carcinoma, Leydig cell tumors, mesothelioma, and leiomyosarcoma are poor expressers of PRAME.

PRAME protein expression in DICER1‐related tumours

“…Some lesions were negative, such as multinodular goitre and carcinoma of the thyroid, while other lesions sometimes showed weak and/or focal staining (<50% positive cells), such as NCMH, intracranial spindle cell sarcoma, Wilms tumour, CN, and PPB type I. The significance of focal staining is unclear but, for the purposes of this study, we elected to consider these lesions as not significant expressors of PRAME, similar to criteria proposed by others [25,39]. The list of positive tumours in our study included pineoblastoma, ciliary body medulloepithelioma, adult pulmonary blastoma, Sertoli–Leydig cell tumour of the ovary, embryonal RMS (cervix and ovary), a paratesticular tumour of probable Müllerian origin [4], PPB types II and III, and ASK.…”

“…Slides were counterstained with haematoxylin. Only nuclear staining was considered positive [39] and the proportion of positive cells was scored as follows: 0, negative; Negative for likely pathogenic or PVs in all coding exons of DICER1 by the techniques indicated as: (a) Fluidigm, (b) Sanger, and (c) whole-exome sequencing. ^^This case did contain a germline DICER1 PV but the absence of a second hit led us to consider this tumor to be unrelated to the DICER1 PV.…”

“…Slides were counterstained with haematoxylin. Only nuclear staining was considered positive [ 39 ] and the proportion of positive cells was scored as follows: 0, negative; 1+, <10% positive cells; 2+, 10–50% positive cells; 3+, >50–90% positive cells; 4+, > 90% positive cells [ 21 ]. Tumours were considered to be PRAME‐ or EZH2‐positive if >50% of cells showed expression.…”

“…Tumours were considered to be PRAME‐ or EZH2‐positive if >50% of cells showed expression. Tumours were also scored by staining intensity (weak, moderate, and strong), but staining intensity was not used to stratify samples as this has not been shown to have any significance [ 25 , 39 ]. All slides were read by a single pathologist (PST).…”

“…PRAME expression is best known in cutaneous melanoma [ 24 , 25 , 26 , 27 ] and uveal melanoma [ 28 ]. However, PRAME expression has also been documented in a wide variety of other malignancies, including non‐small cell lung cancer, squamous cell carcinoma of the head and neck, squamous cell carcinoma of the oesophagus, gastric carcinoma, hepatocellular carcinoma, breast carcinoma, renal cell carcinoma, urothelial bladder carcinoma, ovarian carcinoma, endometrial carcinoma, seminoma, various leukaemias, medulloblastoma, neuroblastoma, synovial sarcoma, myxoid liposarcoma, dedifferentiated liposarcoma, angiosarcoma, malignant peripheral nerve sheath tumour, and osteosarcoma [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ]. PRAME expression is associated with adverse biology of some nature, such as higher tumour grade, higher clinical stage, increased rate of metastases, poor response to chemotherapy, and decreased patient survival.…”