Telomere attrition in isolated high-grade prostatic intraepithelial neoplasia and surrounding stroma is predictive of prostate cancer

Abstract

The causes of early genomic events underlying the development of prostate cancer (CaP) remain unclear. The onset of chromosomal instability is likely to facilitate the formation of crucial genomic aberrations both in the precursor lesion high-grade prostatic intraepithelial neoplasia (HPIN) and in CaP. Instability generated by telomere attrition is one potential mechanism that could initiate chromosomal rearrangements. In this study, normalized telomere length variation was examined in a cohort of 68 men without CaP who had HPIN only on prostatic biopsies. Multiple significant associations between telomere attrition and eventual diagnosis of CaP in the HPIN and in the surrounding stroma were found. Kaplan-Meier analysis of telomere length demonstrated a significantly increased risk for the development of cancer with short telomeres in the surrounding stroma [P = .035; hazard ratio (HR) = 2.12; 95% confidence interval (95% CI) = 0.231-0.956], and a trend for HPIN itself (P = .126; HR = 1.72; 95% CI = 0.287-1.168). Cox regression analysis also demonstrated significance between the time from the original biopsy to the diagnosis of cancer and telomere length in HPIN and in the surrounding stroma. These analyses showed significance, both alone and in combination with baseline prostate-specific antigen, and lend support to the hypothesis that telomere attrition in prostatic preneoplasia may be fundamental to the generation of chromosomal instability and to the emergence of CaP.

Figure 1

A representative example of the analysis used in HPIN biopsies. (A) Areas of interest were identified and corresponding QFISH images were generated on a deeper slice of the tissue, with corresponding areas of stroma (B) and HPIN (C) analyzed. The images have been colored to facilitate visual inspection with telomere PNA probe (Cy3—red) and centromere PNA probe (FITC—green).

Figure 2

To examine the relative amount of chromosomal material in the HPIN versus the amount of chromosomal material in the surrounding stroma, we plotted (A) the frequency distribution of the ratio of centromeric fluorescence intensity measurements in HPIN compared to that in the surrounding stroma. An average increase of 22% (SD 31%) was found in HPIN compared to that found in the surrounding stroma. To examine the relative amount of telomere attrition in the prostate, we plotted (B) the frequency distribution of the ratio of the telomeric fluorescence in HPIN divided by that in the surrounding stroma. As mentioned in the text, an average 64% decrease of the surrounding stroma (SD = 21%) was found. (C) Frequency distribution of normalized telomere values (telomeric fluorescence/centromeric fluorescence) in the HPIN and (D) in the stroma of the study cohort.

Figure 3

(A) Boxplot of relative telomere length in HPIN comparing groups of men who developed cancer and men who did not develop cancer. The thick black line represents median values. The upper border of the blue rectangle represents the 25th percentile, and the lower border represents the 75th percentile. Circles represent outliers based on x 1.5 interquartile range. Bars extending above and below represent the upper and lower limits of data (t-test: P = .03; 95% CI = 0.004–0.080). (B) Boxplot of relative telomere length in the stroma comparing groups of men who developed cancer and men who did not develop cancer. Boxplot variables and numbers are similar to (A) (t-test: P = .04; 95% CI = 0.004–0.188). (C) Kaplan-Meier analysis of HPIN telomere length, stratified by the median value for the time to develop cancer (P = .126; HR = 1.72; 95% CI = 0.287–1.168). (D) Kaplan-Meier analysis of stromal telomere length, stratified by the median value for the time to develop cancer (P = .0346; HR = 2.12; 95% CI = 0.231–0.956).

Figure 4

(A) Relationship between normalized HPIN and stromal telomere length in prostatic biopsies examined. Normalized telomere length reflects telomere intensities controlled for centromeric intensities. R² values are indicated. (B) Boxplots of normalized telomere lengths in HPIN and in the stroma, according to the Gleason score of eventual cancer. Because of limited numbers, cases were grouped according to low (5–6) and high Gleason scores (6–7). Numbers in brackets adjacent to labels on the x-axis represent the number of cases with that outcome in the cohort. Boxplot variables and numbers are similar to those in Figure 3 A. (C) Boxplots represent sites of diagnosis of CaP grouped by their relationship to where the biopsy was analyzed. Boxplot variables and numbers are similar to those in Figure 3 A. X-axis labels refer to the type of analysis: either HPIN or surrounding stroma, with the preceding letters referring to the site of the eventual cancer; eitherthe same site, the same side, or the opposite side of the prostate gland. Numbers in brackets refer to the number of men in those groups.