Atypical cribriform lesions (ACLs) of the prostate consist of cribriform glands lined with cytologically malignant cells with partial or complete basal cell lining. It may represent cribriform "high-grade prostatic intraepithelial neoplasia" (HGPIN) or "intraductal carcinoma of the prostate" (IDC-P), which is almost always associated with clinically aggressive prostate carcinoma (PCa). Distinction between these 2 lesions has profound clinical significance, especially on needle biopsies. However, there are lesions that do not fully satisfy the criteria for IDC-P yet are worse than typical HGPIN and are difficult to distinguish based on morphologic criteria alone.
To better understand the biologic and molecular basis of distinction between cribriform HGPIN and IDC, we used break-apart fluorescence in-situ hybridization assay to assess ETS gene aberrations, a specific and commonest molecular alteration involving PCa, in a cohort of 16 isolated ACL, presumed to be an isolated cribriform HGPIN, and 45 carcinoma-associated ACL (ACL-PCa) on radical prostatectomy specimens, presumed to be spectrum of IDC-P. The latter was further divided into 2 groups: group A with marked nuclear atypia (nuclear size 6xnormal or larger) and/or comedonecrosis (n=21) and group B that did not fulfill these criteria (n=24).
Overall, ERG rearrangement was absent (0 of 16) in isolated cribriform HGPIN, whereas present in 75% (36 of 48) of IDC-P, of which 65% (23 of 36) were through deletion and 35% (13 of 36) through insertion. Notably, 17% (6 of 36) of the IDC-P showed duplication of ERG rearrangement in combination with deletion of 5'-ERG. Hundred percent (34 of 34) of the IDC-P showed concordance of ERG rearrangement status with adjacent invasive carcinoma. There was no difference between the 2 groups of IDC-P lesions regarding prevalence of ERG rearrangement (group A 79% vs. group B 74%) and EDel2+ (20% vs. 15%). No case with ETV1, ETV4, or ETV5 rearrangement was identified.
Our molecular data suggest that isolated cribriform HGPIN and IDC-P are biologically distinct lesions. Majority of ACL-PCa most likely represent intraductal spread of PCa. There is a significant overlap between IDC-P and HGPIN at the lower grade morphologic spectrum. ERG break-apart fluorescence in-situ hybridization assay provides insight into understanding the molecular basis of cribriform HGPIN and IDC-P and has potential clinical implications in their distinction on needle biopsies.