Influence of chronic inflammation on Bcl-2 and PCNA expression in prostate needle biopsy specimens

Abstract

The association between inflammation and cancer has been established in certain forms of human malignancies; however, its role in prostate cancer remains unclear. The present study investigates a possible association between chronic inflammation and the development of epithelial neoplasia in the prostate. Needle biopsy specimens were obtained from patients with serum prostate-specific antigen levels >4 ng/ml, evaluated for morphological findings, and immunostained for Bcl-2 and proliferating cell nuclear antigen (PCNA). Bcl-2 is a survival protein that appears to lie at a nodal point in pathways involved in cell survival, carcinogenesis, and development of therapeutic resistance in certain cancer types. Similarly, PCNA is a critical protein for DNA replication, repair of DNA damage, chromatin structure maintenance, chromosome segregation and cell-cycle progression. The association between these two proteins was examined in prostate tissues with and without chronic inflammation, as well as tissues with and without evidence of neoplastic changes. Of the 106 needle biopsies examined, 18% exhibited atrophy with inflammation. Proliferative inflammatory atrophy/post-atrophic hyperplasia were observed in 42%, high-grade prostatic intraepithelial neoplasia (HGPIN) in 8%, prostatic adenocarcinoma in 11%, and 2% had atypical acinar proliferation suspicious for malignancy. A total of 36 specimens were stained for Bcl-2 and PCNA. Bcl-2 was expressed widely in inflammatory and epithelial tissue; however, more intense expression was observed in the areas of chronic inflammation, predominantly in infiltrating immune cells. The highest proliferation index was observed in the epithelia of HGPIN and cancer. An inverse correlation between the expression of Bcl-2 and the expression of PCNA was observed in the epithelium. The areas of chronic inflammation were associated with increased Bcl-2 expression, whereas the highly proliferative epithelium minimally expressed Bcl-2. These results suggest that Bcl-2 alters the phenotype of particular epithelial cells with a gain in neoplastic characteristics, leading to a likely precursor that may later progress into HGPIN and cancer.

Keywords: chronic inflammation; needle biopsy; post atrophic hyperplasia; proliferative inflammatory atrophy; prostate cancer; prostate-specific antigen.

Figure 1.

Pathological findings in needle-biopsy specimens by hematoxylin and eosin staining. (A) Prostate tissue with an area of SA, and some small and some dilated glands. The glands are lined by small cuboidal cells with bland nuclei and minimal cytoplasm. (B) Prostate tissue with PIA and PAH lesions. Crowded, irregular, atrophic glands with abundant chronic inflammatory infiltrate in the surrounding stroma are visible in the PIA (left), whereas PAH lesions show a dilated central acinus flanked by numerous small and large atrophic acini in a lobular pattern, distorted by sclerotic stroma, which exhibits prominent inflammatory cell infiltrate (right). (C) High-grade PIN involving a large pre-existing duct. Chronic inflammation is present in the stroma (center) is concentrated around another large duct (right). (D) Prostatic adenocarcinoma with cribriform structures. Magnification, ×20. SA, simple atrophy; PIA, proliferative inflammatory atrophy; PAH, post-atrophic hyperplasia; PIN, prostatic intraepithelial neoplasia.

Figure 2.

Immunohistochemical staining for Bcl-2 and PCNA in needle-biopsy specimens within (A) SA, (B) PIA/PAH lesions, (C) high-grade PIN and (D) cancer. Bcl-2 is widely expressed in inflammatory and epithelial tissues of SA and PIA/PAH, with more intense staining in the basal epithelial cells near the areas of chronic inflammation, as well as predominantly in infiltrating immune cells. High expression of PCNA is observed in the proliferating epithelium in high-grade PIN and cancer. Magnification, ×20 (inset, ×40). PCNA, proliferating cell nuclear antigen; SA, simple atrophy; PIA, proliferative inflammatory atrophy; PAH, post-atrophic hyperplasia; PIN, prostatic intraepithelial neoplasia.

Figure 3.

Distribution of Bcl-2 and PCNA in various morphological lesions. (A) A significant difference in Bcl-2 was noted among the four different tissue types (P<0.0001). The pair-wise comparison showed a significant difference in Bcl-2 expression in SA vs. PIA/PAH lesions (P<0.0001); SA vs. HGPIN (P=0.012); PIA/PAH vs. HGPIN (P=0.002); and PIA/PAH vs. cancer (P=0.0009). (B) A significant difference in PCNA expression was noted among the four different tissue types (P<0.0001). The pair-wise comparison revealed a significant difference in PCNA expression in SA vs. PIA/PAH (P=0.0007); SA vs. HGPIN (P=0.002); SA vs. cancer (P=0.002); PIA/PAH vs. HGPIN (P=0.004); PIA/PAH vs. cancer (P=0.0004); and HGPIN vs. cancer (P=0.004). PCNA, proliferating cell nuclear antigen; SA, simple atrophy; PIA, proliferative inflammatory atrophy; PAH, post-atrophic hyperplasia; HGPIN, high-grade prostatic intraepithelial neoplasia; SEM, standard error of the mean.

Figure 4.

Needle-biopsy specimens immunostained for Bcl-2 and PCNA in serial sections. Left and right panels demonstrate serial section from 2 different prostate needle biopsy specimens. (A) Epithelial cells show weak Bcl-2 staining (left panel) and heavy cytoplasmic staining for Bcl-2 (right panel). (B) Needle-biopsy specimens immunostained for PCNA within the serial sections of the same specimen. Intense PCNA in cells which do not express Bcl-2 (left panel) whereas little-to-no expression of PCNA is observed in cells expressing Bcl-2 (right panel). Arrows showing cells expressing high PCNA but not Bcl-2, and vice versa. PCNA, proliferating cell nuclear antigen.

Figure 5.

Scatter plot of inflammation vs. (A) Bcl-2 and (B) PCNA. A strong positive association between inflammation and expression level of Bcl-2 (r=0.882) was observed: The expression of Bcl-2 identified (r=−0.197); however, this was not statistically significant (P=0.249). r-values represent Spearman correlation coefficient. PCNA, proliferating cell nuclear antigen.

Figure 6.

A hypothetical model showing how chronic inflammation leads to cancer development. Under the influence of chronic inflammation epithelial cells acquire increased survival with an increase in Bcl-2 expression. The survival signal alters the phenotype of these particular epithelial cells, which gain neoplastic characteristics, leading to precursors that may later acquire increased proliferation rate leading to cancer development and subsequent progression.