Infiltrative Small Glands In The Prostate

Specimen Type:

Prostate

History:

A 70-year-old male presented with benign prostatic hyperplasia and underwent transurethral resection of the prostate. The specimen consists of numerous chips of pink-tan prostatic tissue in aggregate weighing 21.11gm and measuring 6.0 x 6.0 x 4.0 cm. Representative sections were submitted.

Pathologic Features:

The sections reveal a large number of crowded small glands mainly proliferating in a lobular fashion (Fig 1). Similar glands are also seen infiltrating between benign prostatic glands (Fig 2). Most glands appear to be solid while few glands have narrowly opened lumen (Fig 3). The glands are lined by more than one layer of cells even in very small-acini (Fig 4, 5, 6). The lining cells toward lumen is columnar-type with abundant cytoplasm while the cells in the periphery have relatively less cytoplasm (Fiag 7). Immunostains for 34BE12 and p63 highlight a circumferential pattern of basal cells in the outer layers of glands (Fig 8), and this feature is very prominent in some areas (Fig 9); the inner layer of cells stain positively for racemase (Fig 8, 9) and PAP (Fig 10).

Differential Diagnosis:

  • Atypical adenomatous hyperplasia
  • Basal cell hyperplasia
  • Basaloid/adenoid cystic carcinoma

Atypical adenomatous hyperplasia (AAH): AAH, also known as adenosis, is a small glandular proliferation that has been described as “a localized proliferation of small glands within the prostate that may be mistaken for carcinoma”. This is invariably an incidental histologic finding in TURP or prostatectomy specimen. Microscopically, AAH typically is a well-circumscribed collection of densely packed small, pale, acini, which merge with larger, more complex glands. The periphery of the aggregate is characteristically rounded, but in a minority of cases, the small acini can extend into surrounding stroma in an infiltrative pattern. Many of these small glands are round and regular or elongated, with open lumens. The small acini have a fragmented or discontinuous basal cell layer which can be highlighted by basal cell marker through immunohistochemical staining. The nuclei should be bland with little variation in size and shape, and any detectable nuclei should be small.

Basal cell hyperplasia: Though often viewed as a transition zone proliferation in the setting usual epithelial hyperplasia, it can be also found in the peripheral zone, associated with inflammation. In addition, it is a common reactive response to therapy effect on the prostate. Histologically, basal cell hyperplasia often is multifocal, and characterized by two and more layers of basal cells with a range of growth features. These glands or nests often are focal but can form nodules. In some cases, the glands can appear to infiltrate between normal glands. The patterns of hyperplastic basal cells vary from focal, eccentric, partial gland involvement to a symmetric, circumferential proliferation with central retention of secretory cell layer to nearly complete luminal obliteration. Solid, small nests are also common.

Basal cell prominence is an apparent increase in number of basal cells, which are still in a single layer rather than forming multiple layers. Although this prominence may represent basal cell hyperplasia, the current definition for basal cell hyperplasia requires two or more layers of basal cells.

Basaloid/adenoid cystic carcinoma: Basal cell carcinomas are rare tumors with less than 100 reported cases. Clinically, patients present with obstructive and irritative symptoms. Microscopically, the basaloid cell proliferation should be infiltrative with a prominent cribriform architecture. Cordlike, glandular, and nested basaloid patterns can also be present. The cribriform spaces often contain basement membrane-like material or basophilic mucinous secretions. Cytologically, tumor cells are generally small with scant amount of cytoplasm and finely stippled chromatin. Apoptotic bodies are commonly present, and nuclear atypia and mitotic figures are variable. Necrosis, perineural invasion, and vascular invasion may be present. These tumors predominantly show an indolent course with local infiltrative behavior. A small subset behaves aggressively with local recurrences and distant metastases.

Diagnosis:

Florid basal cell hyperplasia (BCH)

  • An incidental histologic finding, a mimicker of cancer; no clinical significance
  • Lobular growth pattern; a small collection of glands between normal glands may appear to be infiltrative
  • Glands lined by two or more layer of basal cells;
  • Major patterns: Glands and solid nests; Minor patterns: Cribriform, pseudocribriform and cords
  • Cytologically, cells have scant cytoplasm and bland nuclear features.

Comment: Basal cell hyperplasia, a mimicker of cancer, can be easily recognized by a collection of solid nests arranged in a lobular pattern even though glandular structures of variable amount may often be present. The presence of a small number of nests/glands between normal glands, which appear to be infiltrative, is not uncommon (reference 1). In some areas, the innermost secretory layer of glands which is PSA positive is retained and usually displays atrophic features instead of proliferative due to the predominance of basal cell proliferation. However, in rare cases of basal cell hyperplasia as seen in this case, the secretory layer can be proliferative and becomes fairly prominent, which is high columnar in appearance and positive for racemase. Distinction from basal cell carcinoma can be difficult when small biopsy is encountered. Diagnosis of basal cell carcinoma can be facilitated by identification of large acini that are often dilated and exhibited extensive interanastomoses, prominent intraglandular hyalinization, perineural invasion, and extraprostatic extension.

References:

  1. Hosler GA, et al. Basal cell hyperplasia: an unusual diagnostic dilemma on prostate needle biopsies. Hum Pathol. 2005 May;36 (5):480-5.
  2. Iczkowski KA, Ferguson KL, Grier DD, Hossain D, Banerjee SS, McNeal JE, Bostwick DG. Adenoid cystic/basal cell carcinoma of the prostate: clinicopathologic findings in 19 cases. Am J Surg Pathol. 2003 Dec;27(12):1523-9.
  3. McKenney JK, et al. Basal cell proliferations of the prostate other than usual basal cell hyperplasia: a clinicopathologic study of 23 cases, including four carcinomas, with a proposed classification. Am J Surg Pathol. 2004 Oct;28(10):1289-98.