Intraductal Carcinoma of the Prostate: To Grade or Not to Grade

Abstract

Intraductal carcinoma of the prostate (IDC-P) is a distinct tumor type characterized by an expansile growth of atypical glandular epithelial cells within pre-existing prostate glands and ducts and has significant implications on clinical outcomes and patient management. There is an agreement that isolated IDC-P should not be graded, and IDC-P should be reported with a comment on its clinical significance. However, whether IDC-P should be factored into Grade Group (GG) in the presence of concurrent prostate cancer (PCa) has been debated vigorously. The contradicting opinions were promulgated when the Genitourinary Pathology Society (GUPS) and the International Society of Urological Pathologists (ISUP) published their recommendations for this issue. When IDC-P is present with PCa, the ISUP recommends incorporating it in the GG for the entire case, whereas the GUPS recommends excluding it from the final GG. Consequently, pathologists and clinicians are faced with the conundrum of conflicting recommendations. In this review article, the authors evaluate the magnitude of discrepant GG between the two grading methods, explore the rationales behind the differing views of the two urological societies, present the current reporting practices for IDC-P, and propose a provisional and pragmatic guide to alleviate the dilemma of which recommendation to follow.

Keywords: GUPS; IDC-P; ISUP; basal cell markers; immunohistochemistry; in situ; intraductal carcinoma of the prostate; precursor; recommendation; reporting practice.

Figure 1

Isolated IDC-P without concomitant prostate cancer in a prostate biopsy (A,B). The IDC-P glands have residual basal cells positive for basal cell markers (brown stains) and are also positive for AMACR (red stain) (C). Isolated IDC-P is associated with unsampled GG ≥ 2 PCa in the majority of cases, although no invasive or only GG1 PCa is found in subsequent RPs in approximately 10% of cases.

Figure 1

Isolated IDC-P without concomitant prostate cancer in a prostate biopsy (A,B). The IDC-P glands have residual basal cells positive for basal cell markers (brown stains) and are also positive for AMACR (red stain) (C). Isolated IDC-P is associated with unsampled GG ≥ 2 PCa in the majority of cases, although no invasive or only GG1 PCa is found in subsequent RPs in approximately 10% of cases.

Figure 2

Usual-type IDC-P with GG5 prostate cancer. IDC-P glands show cribriform morphology and are surrounded by invasive cancer glands (A). IDC-P glands have residual basal cells highlighted by basal cell marker P63 (brown stain), while the cancer glands lack basal cells (B).

Figure 2

Usual-type IDC-P with GG5 prostate cancer. IDC-P glands show cribriform morphology and are surrounded by invasive cancer glands (A). IDC-P glands have residual basal cells highlighted by basal cell marker P63 (brown stain), while the cancer glands lack basal cells (B).