Apoptosis, p53, bcl-2, and Ki-67 in invasive bladder carcinoma: possible predictors for response to radiochemotherapy and successful bladder preservation

Abstract

Purpose: Several groups have reported the value of bladder preservation by a combined treatment protocol, including transurethral resection (TUR-B) and radiochemotherapy (RCT). As more experience is acquired with organ-sparing treatment, patient selection should be optimized. The purpose of this study was to investigate the role of several biologic markers that may predict response to RCT in muscle-invasive bladder carcinoma.

Methods and Materials: The apoptotic index (AI), Ki-67, p53, and bcl-2 were evaluated by immunohistochemistry on pretreatment biopsies from 70 patients treated for invasive bladder cancer by TUR-B and RCT. Expression of each marker was correlated with initial response, local control, and cancer-specific survival with preserved bladder. An exploratory multivariate analysis was also performed that included clinical and immunohistochemical variables.

Results: A high AI (> median = 1.6%) and a high Ki-67 index (> median = 8.8%), but not the p53- and bcl-2 expression, were significantly related to initial complete response (CR) and local control with preserved bladder after 5 years. When the AI and Ki-67 expression were considered simultaneously, the association with initial CR (p < 0.001), local control (p = 0.0002), and cancer-specific survival with preserved bladder (p = 0.008) was highly significant. In an exploratory multivariate analysis (final model), only AI, Ki-67, and the combined AI/Ki-67 variable retained significance for local control with preserved bladder at 5 years.

Conclusion: Patients with a high spontaneous AI and a high pretreatment Ki-67 index should be considered preferentially for treatment with RCT, whereas tumors with low proliferation and low levels of apoptosis are less likely to respond to RCT.

Introduction

The optimal treatment of muscle-invasive bladder cancer has been a subject of continuous controversy. In the United States as well as in Europe, the usual approach has been radical cystectomy. Sophisticated techniques for urinary diversion have been developed; however, even a neovesica cannot substitute for the patient’s original bladder. Several groups have reported the value of combined modality therapy with selective bladder preservation to optimize quality of life without compromising survival 1, 2, 3, 4, 5, 6. With these programs, cystectomy has been reserved for patients with incomplete response or local failure following transurethral resection (TUR-B), radiation therapy (RT), and systemic chemotherapy.

As more experience is acquired with organ-sparing treatment, it is clear that patient selection must be optimized. Clinical criteria helpful in determining patients for bladder preservation include such variables as small tumor size and a possible complete TUR-B prior to radiochemotherapy (RCT) (7). Tumor heterogeneity, however, is so great in bladder cancer that conventional histopathologic classification is inadequate for predicting the response to RCT for individual lesions. Molecular markers that may better stratify and identify a tumor’s true malignant potential as well as its response to specific cytotoxic therapies are sorely needed.

Several markers have been linked to radio- and chemosensitivity of bladder cancer cells, including p53, pRb, and bcl-2 as key protein regulators of the cell-cycle and the apoptotic pathway as well as markers of tumor cell proliferation 8, 9, 10. Apoptosis has now been recognized as an important mechanism of radiation- and chemotherapy-induced cell death. The predictive value of the baseline levels of apoptosis for the response to RT alone has been demonstrated for cervical 11, 12, rectal (13), and bladder carcinomas (14). The wild-type p53 is essential for cell growth regulation and balance between apoptosis and G1 arrest with repair of DNA damage. Overexpression of altered p53 has been detected in a high percentage of transitional-cell bladder carcinomas and has been shown to be an independent predictor of recurrence and overall survival in invasive bladder cancer treated with radical cystectomy alone (15). However, in vivo and in vitro results concerning the effect of altered p53 expression on radiation- and drug-resistance are inconclusive. In certain cells the loss of p53 function has been reported to increase radioresistance 16, 17. On the other hand, in a study using human bladder cell lines p53 mutation was associated with increased radiosensitivity (18). Likewise, some authors found no predictive value of p53 status for bladder cancer response to radiotherapy in the clinical setting 19, 20; others reported that p53 can help select patients for bladder preservation by a regimen of neoadjuvant chemotherapy (21). Bcl-2 also affects cell death through interference with the apoptotic pathway. The increased expression of bcl-2 has been found to alter tumor sensitivity to chemotherapy and radiation 22, 23. Pollack et al. reported that bcl-2 overexpression was associated with impaired radiation response in patients with bladder cancer treated with a regimen of preoperative radiotherapy (23). The significance of this anti-apoptotic protein as well as the role of proliferation as measured by the Ki-67-labeling index in predicting local control in bladder cancer treated by a combination of radio- and chemotherapy remains to be established. Correlating the expression of several molecular markers and clinicopathologic factors and elucidating their interrelationships may finally help to identify subgroups of patients that will most probably benefit from bladder preservation by combined modality treatment.