Table IV.

Rationale behind the Recommendations to Grade or Not Grade IDC-P ⁴¹.

Issues	GUPS	ISUP
Historical studies	The proportion of cases that including or excluding IDC-P would have changed the grade in these studies is very small and would not have any significant impact.	These studies were based on morphology without the use of IHC and would have included IDC-P in the grading.
IDC-P could represent a precursor lesion	Grading IDC-P will result in overgrading in this small subset of patients who has IDC-P with no or at most low-grade PCa.	Guidelines should not be based on this rare scenario; not grading IDC-P can result in undergrading or separate comments on IDC-P being disregarded by clinicians.
IHC for basal cell stains	Basal cell stain is required for accurate grading in as few as 1 in 150 cases (< 1%) in Dr. Epstein’s routine practice.	Excluding IDC-P from invasive PCa will require greater use of expensive IHC, and the absence of basal cell staining does not entirely exclude IDC-P due to the patchy distribution of basal cells.
A study showing that grading IDC-P improves prognostication 82	This study has limitations, e.g., flaws from including cases with sextant (6-core) biopsy, small sample size compared to the initial study describing Grade Groups, and not distinguishing IDC-P and cribriform carcinoma.	This study showed that incorporating IDC-P and cribriform carcinoma into Grade Groups improved the predictive value of the system for cancer-specific survival and metastasis-free survival.

IDC-P, intraductal carcinoma of the prostate; IHC, immunohistochemistry; PCa, prostatic adenocarcinoma.