Prognostic Markers in Prostate Cancer
A review article on the most current predictive tools for staging, cancer recurrence, and survival.
by David G. Bostwick, M.D., M.B.A. & Junqi Qian, M.D.
High-grade prostatic intraepithelial neoplasia (PIN) is now accepted as the most likely pre-invasive stage of adenocarcinoma, a decade after its first formal description. PIN has a high predictive value as a marker for adenocarcinoma, and its identification warrants repeat biopsy for concurrent or subsequent invasive carcinoma. The only method of detection is biopsy; PIN does not significantly elevate serum PSA concentration or its derivatives and cannot be detected by ultrasound. Most studies suggest that most patients with PIN will develop carcinoma within ten years. PIN is associated with progressive abnormalities of phenotype and genotype that are similar to cancer rather than normal prostatic epithelium, indicating impairment of cell differentiation with advancing stages of prostatic carcinogenesis. Androgen deprivation therapy decreases the prevalence and extent of PIN, suggesting that this form of treatment may play a role in chemoprevention.
DNA ploidy analysis by digital image analysis is usually performed in routinely processed tissue sections stained by the Feulgen method. The Feulgen stain stoichiometrically binds to hydrolyzed nucleic acids, coloring nuclei blue according to the amount of DNA present (1-3). A good correlation exists between DNA ploidy and cancer histologic grade, and DNA ploidy adds clinically useful predictive information for some cancer patients (1-3). DNA ploidy analysis of prostate cancer provides important predictive information which supplements histopathologic examination. Patients with diploid tumors have a more favorable outcome than those with aneuploid tumors. Among patients with lymph node metastases treated with radical prostatectomy and androgen deprivation therapy, those with diploid tumors may survive 20 years or more, whereas those with aneuploid tumors may die within 5 years (4). DNA ploidy analysis of needle biopsies is prognostically useful, particularly when combined with the proliferative fraction (5).
Proliferating cell nuclear antigen (PCNA)
Proliferating cell nuclear antigen (PCNA) is an auxiliary protein for DNA polymerase which reaches maximal expression during the S phase of the cell cycle (6). Hence, PCNA has been widely used as an index of the proliferative activity of cancers. The PCNA labelling index is reported to be lowest in benign normal prostatic epithelium and organ-confined cancer but to increase progressively from well- through poorly-differentiated invasive prostate cancer, although there is wide variance (7). The correlation of PCNA index is strong with cancer stage (6-8). Hence, high PCNA labelling indices may indicate progression of prostate cancer (9-10), and may be an independent prognostic indicator (9).
Ki-67 and MIB-1
The Ki-67 antibody recognizes a nuclear antigen present in proliferating cells, but absent is resting cells (11). Since the original antibodies to Ki-67 exhibited only poor immunoreactivity in fixed paraffin-embedded tissues, the MIB-1 antibody was developed against recombinant parts of the Ki-67 antigen for specific use on formalin-fixed and paraffin wax-embedded tissues (11). In prostate cancer, a high proliferation index for either antibody appears to addlittle predictive information for patient outcome above the traditional indicators of Gleason score, pathologic stage, and DNA ploidy (12-14). However, the Ki-67 labelling index may discriminate between organ confined and metastatic cancer (14). Hence, elevation in the proliferation indices of Ki-67/MIB-1 appear to reflect progression (15, 16). This is further reflected in an association between expression of Ki-67 and the epidermal growth factor receptor (17), mutant p53 (18, 19), particular chromosomal aberrations (20), and perineural invasion (21). Taken together, all of these findings suggest that Ki-67 expression may be a weak prognostic indicator of recurrence (22, 23), progression (16, 24) and survival (19, 23, 25).
Microvessel Density (MVD)
The microvessel density (MVD) is usually calculated by counting vascular cross-sectional profiles within a 0.81-1mm2 area. The vascular endothelium can be stained with antibody CD34 (26). Microvessel density analysis offers promise for predicting pathologic stage and patient outcome in prostate cancer. Most of the prostatectomy studies found a positive correlation of MVD with pathologic stage. MVD in cancer on biopsy showed a positive correlation with matched prostatectomies, and was an independent predictor of extraprostatic extension (27, 28). Microvascular invasion also correlated with stage, grade, and other parameters stage (28-30). There is generally good agreement about prediction of cancer recurrence and patient survival based on MVD (31-34). The cumulative evidence suggests that there is an important role for microvessel density analysis in management of select patients with prostate cancer.
Bcl-2 protein, functions as blockers of apoptosis and programmed cell death. Over expression of Bcl-2 has been associated with breast carcinoma, neoplastic cells of lymphomas, and a number of non-hematopoietic tumor cells (35, 36). Expression of bcl-2 is normally restricted to the basal cell layer of the normal and hyperplastic prostatic epithelium (37, 38). However, overexpression of bcl-2 is present in high-grade prostatic intraepithelial neoplasia (37, 39). A recent study found that over 70% of prostate carcinomas were bcl-2 negative, 18% had weak expression, and 11% exhibited strong expression. Expression of bcl-2 was correlated with high stage, metastases, and high grade. Androgen deprivation therapy increased bcl-2 expression in cancer, suggesting that these cells develop resistance to apoptotic signals (37, 39). In hormone-refractory prostate cancer, heterogeneous staining was observed in most specimens, with expression retained in clusters of cancer cells. In bone marrow metastases after androgen deprivation, approximately 30% of cancers expressed bcl-2, but expression did not correlate with survival (40, 41). In conclusion, expression of bcl-2 varies greatly in localized prostate cancer, but is consistently expressed in prostate cancer cells after androgen deprivation and in those that are hormone-refractory (37, 40, 41). These data support the concept that bcl-2 is causally linked to apoptotic resistance in prostatic cancer cells.
The p53 tumor suppressor gene functions as a regulator of the cell cycle. In normal cells and tissue, p53 protein has a very short half-life and attains such a low level that is not detectable immunohistochemically. The p53 gene abnormalities are associated with many human malignancies. However, there is a much lower incidence of p53 genetic alterations in primary prostate cancer than in bladder, colon, lung, and breast cancer (43). Nuclear accumulation of p53 protein is strongly associated with missense p53 mutations (44). Most immunohistochemical studies concluded that mutant p53 expression is a late event in localized prostate cancer (45-47), usually present in higher (> 7) grade cancer (44, 48, 49).
Moreover, the frequency of mutant p53 expression is elevated in untreated metastatic cancer (19, 43, 50) hormone refractory cancer (44, 46, 50) and recurrent cancer (19, 49). A recent study showed that staining of prostatectomies correlated well with PSA recurrence for (p = 0.004) and bcl-2 (p = 0.001), indicating that p53 and bcl-2 biomarkers appear to be important to predict recurrence of prostate cancer (49). The availability of more refined prognostically important biological variables in addition to established prognostic factors like tumor stage or Gleason score might help decision making in patients at high risk for the development of local recurrence or systemic tumor progression.
The cyclin-dependent kinase inhibitor (p27Kip1) also negatively regulates cell proliferation by mediating cell cycle arrest in G1. p27Kip1 protein expression can be detected in almost 100% of normal prostatic epithelium, but decreases in cancer with higher Gleason score and seminal vesicle involvement (51, 52, 53, 54). A recent study showed that patients with loss of p27Kip1 protein expression or a relative amount of <10% of positively stained tumor cells developed recurrent disease in contrast to patients with retained p27Kip1 protein expression (> or =10% of positively stained tumor cells). In a multivariate analysis, loss of p27Kip1 protein expression was identified as the only independent prognostic parameter for recurrence-free survival. These results suggest that decreased p27Kip1 expression may be an independent predictor for cancer recurrence and long-term survival of prostate cancer patients (51, 52, 53, 54).
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