Residency · Residency · Pathology

Prostate Needle Biopsy and Gleason Grading

Overview

Prostate needle biopsy is one of the highest-volume specimens in surgical pathology. The pathologist must accurately identify carcinoma, distinguish it from mimickers, apply the current ISUP Grade Group system, and report quantitative features that guide clinical management including active surveillance eligibility.

Normal Prostate Anatomy

The prostate has a glandular architecture composed of secretory cells (luminal, PSA-positive, AMACR-negative), basal cells (p63-positive, HMWCK/34betaE12-positive, CK5/6-positive), and rare neuroendocrine cells. The peripheral zone harbors 70 percent of cancers, while the transition zone gives rise to BPH nodules and approximately 20 percent of cancers. The basal cell layer is critically important: it is present in benign glands and absent in carcinoma. Corpora amylacea (laminated eosinophilic secretions) are found in benign glands and are rare in carcinoma.

Prostatic Adenocarcinoma

Diagnostic Criteria

The diagnosis of prostatic adenocarcinoma rests on several features: small crowded glands infiltrating between benign glands, absence of the basal cell layer (confirmed by p63 and/or HMWCK immunohistochemistry), nuclear enlargement with prominent nucleoli (macronucleoli of 1 micrometer or greater), AMACR (P504S) positivity (cytoplasmic granular staining present in approximately 80 percent of cancers), amphophilic cytoplasm (darker than benign), crystalloids (bright eosinophilic refractile structures in gland lumina), intraluminal blue mucin (acidic mucin), perineural invasion (diagnostic of malignancy when identified), and collagenous micronodules (mucinous fibroplasia).

IHC Panel for Small Foci

Basal cell markers (p63 for nuclear staining, HMWCK/34betaE12 for cytoplasmic staining) are absent in carcinoma and present in benign glands. AMACR (P504S) is positive in carcinoma and negative in benign tissue with certain exceptions. A triple cocktail (p63/HMWCK/AMACR) on a single slide provides an efficient diagnostic approach. Pitfalls include partial basal cell loss in high-grade PIN and atrophy, and AMACR positivity in nephrogenic adenoma, partial atrophy, and some benign mimickers.

ISUP Grade Group System (Modified Gleason)

Gleason Patterns

Patterns 1 and 2 are no longer assigned on needle biopsy (only on resection, and rarely). They represented well-circumscribed nodules of uniform glands that are essentially never seen on core biopsy.

Pattern 3 consists of discrete, individual, well-formed glands that infiltrate between benign glands. Each gland varies in size but has a complete lumen. There are no poorly formed glands, fused glands, cribriform architecture, or glomeruloid features. This is the pattern that defines "low-risk" disease.

Pattern 4 encompasses fused glands (poorly defined glandular lumina with confluent growth), poorly formed glands (incomplete luminal formation with barely discernible lumina), cribriform glands (large glands with multiple punched-out lumina in a sieve-like pattern, associated with aggressive behavior and adverse outcomes), and glomeruloid structures (intraluminal cribriform proliferations attached to one side of the gland).

Pattern 5 includes solid sheets, cords, or single cells without glandular differentiation, comedonecrosis within cribriform glands (classified as Gleason 5 by convention), and signet ring cell features. It is the most aggressive pattern.

ISUP Grade Groups

Grading Rules for Needle Biopsy

The primary and secondary patterns (most prevalent and second most prevalent) are assigned. If only one pattern is present, it serves as both primary and secondary (for example, 3+3). When three patterns are present, the most common and the highest grade are reported (not the second most common). Tertiary pattern 5 should be reported separately even if it represents less than 5 percent of the tumor. Cribriform pattern 4 should be specifically mentioned in the report given its association with adverse outcomes independent of grade group. Each core should be graded individually.

Mimickers of Prostatic Adenocarcinoma

Atypical Small Acinar Proliferation (ASAP)

ASAP is not a pathologic entity but a diagnostic category indicating that a small focus of atypical glands is suspicious for but not diagnostic of carcinoma. The glands may be too few, IHC may be equivocal, or atypia may be insufficient for a definitive diagnosis. Repeat biopsy is recommended, as approximately 40 percent will show carcinoma on rebiopsy.

High-Grade Prostatic Intraepithelial Neoplasia (HGPIN)

HGPIN shows large glands with an intact or fragmented basal cell layer, nuclear enlargement with prominent nucleoli in luminal cells, and architectural patterns (tufting, micropapillary, cribriform, flat). Basal cells are present (p63/HMWCK-positive), distinguishing it from invasive carcinoma. Isolated HGPIN on initial biopsy no longer routinely warrants immediate rebiopsy in most guidelines.

Intraductal Carcinoma of the Prostate (IDC-P)

IDC-P is a malignant epithelial proliferation within pre-existing prostatic ducts that retains the basal cell layer (p63/HMWCK-positive), similar to HGPIN. It is distinguished from HGPIN by larger glands, dense cribriform or solid architecture, marked nuclear atypia, and comedonecrosis. It is almost always associated with high-grade invasive carcinoma (Gleason 4+4 or higher). When found without invasive carcinoma on biopsy, it is associated with aggressive disease on resection and should be treated as high-grade cancer.

Benign Mimickers

Atrophy shows small glands with scant cytoplasm but with basal cells present, and may be AMACR-positive. Post-atrophic hyperplasia (PAH) shows lobular clusters of small glands with atrophic cytoplasm. Adenosis (atypical adenomatous hyperplasia) is a lobular proliferation of small glands with partial basal cells that is crowded but benign. Seminal vesicle/ejaculatory duct epithelium has nuclear atypia with lipofuscin pigment and is PAX2/PAX8-positive but not PSA/NKX3.1-positive. Nephrogenic adenoma shows small tubules in the periurethral region that are PAX2/PAX8-positive and AMACR-positive but p63-negative and PSA-negative. Basal cell hyperplasia is a proliferation of basal cells in nests (p63/HMWCK-positive). Verumontanum mucosal gland hyperplasia shows crowded small glands at the verumontanum (PSA-positive, basal cells present).

Reporting Requirements for Prostate Needle Biopsy

Essential elements include Gleason score and ISUP Grade Group per core (or per site), number and percentage of positive cores, percentage of cancer involvement per core (linear extent in mm), presence of cribriform pattern (specified), perineural invasion, extraprostatic extension (rare on biopsy, identified by involvement of periprostatic fat), intraductal carcinoma (if present), and seminal vesicle invasion (if sampled).

Active Surveillance Criteria (Pathologic)

Pathologic criteria for active surveillance eligibility include Grade Group 1 (Gleason 3+3=6), low volume (2 to 3 or fewer positive cores with 50 percent or less involvement per core, though criteria vary), no intraductal carcinoma, and no cribriform pattern 4. Confirmatory biopsy within 6 to 12 months and MRI-targeted biopsy integration are part of the protocol.

<image>A medical illustration of Gleason grading patterns. Panel A (Pattern 3): Well-formed individual glands of varying sizes infiltrating between benign glands, each gland with a complete well-defined lumen, nuclear enlargement with prominent nucleoli. Panel B (Pattern 4): Fused glands with ill-defined lumina and poorly formed glands (top); cribriform glands with multiple punched-out lumina forming a sieve-like pattern (middle); glomeruloid structure with intraluminal cribriform proliferation (bottom). Panel C (Pattern 5): Solid sheets of tumor cells without glandular differentiation (top); cribriform gland with central comedonecrosis (bottom). Panel D: Intraductal carcinoma showing a large duct with dense cribriform proliferation and comedonecrosis, with p63 IHC inset showing retained basal cells around the duct.</image>

<image>A medical illustration of prostate cancer mimickers and the IHC panel. Panel A (ASAP): A tiny focus of atypical glands with limited tissue for assessment, triple stain inset showing absent p63/HMWCK with positive AMACR. Panel B (High-grade PIN): Large glands with tufting/micropapillary luminal cell proliferation and prominent nucleoli, p63 IHC showing retained basal cells (positive). Panel C (Atrophy mimicking cancer): Small glands with scant cytoplasm, p63 IHC showing intact basal cell layer. Panel D (Adenosis): Lobular proliferation of crowded small glands, p63 IHC showing partial/patchy basal cells at the periphery of the lobule. Each panel annotated with the key distinguishing features from carcinoma.</image>

<image>A medical illustration of the ISUP Grade Group system with clinical correlation. Five panels showing representative histology for each Grade Group: GG1 (Gleason 3+3=6, only well-formed glands), GG2 (Gleason 3+4=7, predominantly pattern 3 with minority fused/cribriform glands), GG3 (Gleason 4+3=7, predominantly pattern 4 with lesser pattern 3), GG4 (Gleason 4+4=8, predominantly pattern 4 with cribriform and fused glands), GG5 (Gleason 4+5=9, pattern 5 with solid sheets and comedonecrosis). A bar graph showing 5-year biochemical recurrence-free survival for each group after radical prostatectomy.</image>

Clinical Pearls

Cribriform pattern 4 should always be specifically reported because it is independently associated with metastasis, biochemical recurrence, and cancer-specific mortality even compared to other Gleason pattern 4 morphologies (fused, poorly formed). Its presence generally excludes patients from active surveillance. The distinction between HGPIN and intraductal carcinoma is clinically critical: HGPIN is a precursor lesion of uncertain significance, while IDC-P is almost always associated with high-grade invasive carcinoma and warrants treatment even if invasive carcinoma is not identified on the biopsy.

ASAP is not a diagnosis but a diagnostic category indicating insufficient evidence for a definitive cancer diagnosis. It carries an approximately 40 percent cancer detection rate on repeat biopsy and should always be communicated clearly to the urologist. Grade Group 1 (Gleason 3+3=6) prostate cancer has essentially zero metastatic potential, supporting the rationale for active surveillance and the ongoing debate about whether these lesions should be labeled "cancer."

When encountering small atypical glands on biopsy, the most useful IHC approach is a triple cocktail (p63 plus HMWCK plus AMACR) on a single slide: loss of basal markers with positive AMACR strongly supports carcinoma, while retained basal cells favor a benign process. Perineural invasion on needle biopsy does not upstage the tumor but is associated with extraprostatic extension on radical prostatectomy and may influence the decision to perform nerve-sparing surgery.

References

• Epstein JI, et al. The 2014 International Society of Urological Pathology (ISUP) consensus conference on Gleason grading of prostatic carcinoma. Am J Surg Pathol. 2016;40(2):244-252.
• Egevad L, et al. International Society of Urological Pathology (ISUP) grading of prostate cancer -- An ISUP consensus on contemporary grading. APMIS. 2016;124(6):433-435.
• Humphrey PA, et al. The 2016 WHO Classification of Tumours of the Urinary System and Male Genital Organs. Eur Urol. 2016;70(1):106-119.
• Kweldam CF, et al. Cribriform growth is highly predictive for postoperative metastasis and disease-specific death in Gleason score 7 prostate cancer. Mod Pathol. 2015;28(3):457-464.
• Amin MB, et al. AJCC Cancer Staging Manual. 8th ed. Springer; 2017.

Read this lecture as Markdown