August 2026

Author: Theodorus H. Van der Kwast MD, PhD Department of Pathology, University Health Network, Toronto, ON

 

64 year-old man underwent radical prostatectomy for an ISUP grade 3 prostate cancer, incidental microscopic finding right mid anterior in anterior fibromuscular stroma

 

Gross findings

Well-circumscribed cellular nodule, approximately 7 mm in diameter

Microscopic findings

Well-circumscribed nodular area mid-anterior in the prostate (Figure 1)

 

The nodule is composed of densely packed glands (Figure 2) 

Cellular stroma and glands are closely admixed (Figure 3)

Glands are small-sized, have pale cytoplasm and somewhat enlarged nuclei with rather inconspicuous nucleoli (Figure 4)

Area with myxoid appearance is visible (Figure 5)

Immunohistochemical and Molecular findings

Positive:

PSA – glandular cells

HMWK

Smooth muscle actin (Figure 6)

S100 (Figures 7 and 8)

Test yourself. What diagnosis would you give to this case?

  • Adenosis (atypical adenomatous hyperplasia)
  • Adenocarcinoma, Gleason grade 1
  • Nephrogenic remnants
  • Sclerosing adenosis
  • Blue nevus

Diagnosis by author: 

Sclerosing adenosis

Discussion of case

Sclerosing adenosis is a benign lesion of the transition zone of the prostate, characterized by a cellular nodule of mostly small-sized glands and solid nests in a cellular spindle-cell stroma (1). Characteristically, the basal cell layer shows myoepithelial differentiation and is positive for S100, smooth muscle actin, and HMWK (2). Cytologic atypia is minimal, but rare cases may demonstrate nuclear atypia (3).

 

Major Differential Diagnosis

Adenosis (atypical adenomatous hyperplasia)
Nodular growth, transition zone localization
Sporadic basal cells lining small-sized (pale) glands
Lacks intervening dense cellular stroma and myxoid areas

 

Adenocarcinoma
No basal or myo-epithelial cells lining acini
More conspicuous nucleoli

 

Nephrogenic remnants
Lobule of small-sized uniform glands with characteristic eosinophilic secretion

 

Blue nevus
Pigmented (S100 positive) stroma cells
No glandular component

 

Key References

Young RH, Clement PB. Sclerosing adenosis of the prostate. Arch Pathol Lab Med. 1987; 111: 363-6.

Grignon DJ, Ro JY, Srigley JR, Troncoso P, Raymond AK, Ayala AG. Sclerosing adenosis of the prostate gland. A lesion showing myoepithelial differentiation. Am J Surg Pathol. 1992; 16: 383-91.

Cheng L, Bostwick DG. Atypical sclerosing adenosis of the prostate: a rare mimic of adenocarcinoma. Histopathology. 2010; 56: 627-31.