Original studySerum M65 as a Biomarker for Metastatic Renal Cell Carcinoma
Introduction
Renal cell carcinoma (RCC) is the most common type of kidney cancer. Recent developments in the molecular biology of RCC have enabled the identification of multiple pathways related to the development of this cancer. Several prognostic factors can help discriminate between favorable and unfavorable RCC phenotypes. Of those, various clinical, pathological, and biological markers have been tested and validated, and they are used in predictive and prognostic models. Nonetheless, researchers are still searching for informative markers that predict the response to targeted therapies. Cytokeratin 18 (CK18) is the major component of intermediate filaments in epithelial cells, including those in the liver, lung, kidney, pancreas, mammary gland, and in tumors that arise from these organs.1 CK18 expression has been detected in tissue blocks from some patients with RCC. In a clinical study by Skinnider et al,2 renal epithelial neoplasms expressed CK18. Recently, Messai et al1 evaluated the expression pattern of CK18 in RCC patients and its prognostic relevance. Their data indicated that CK18 mRNA and protein levels increased with advanced stage and grade of the disease.
Renal cell carcinoma is believed to originate from the proximal tubule epithelium.3, 4 A novel method based on the measurement of different molecular forms of CK18 can be used to investigate the modes of epithelial cell death. CK18 is cleaved by caspases during apoptosis, and its fragments are released into the serum.5, 6 Intact or caspase-cleaved forms of CK18 are usually accepted as markers of cell death in the malignant transformation.7 M30 and M65 are the caspase-cleaved and intact forms of CK18, respectively, and they can be detected in the circulation by enzyme-linked immunosorbent assay (ELISA).8, 9, 10 M30 is the monoclonal antibody that recognizes the caspase-cleaved CK18 fragments so it is the selective biomarker of epithelial apoptosis.10 Monoclonal antibody M65 recognizes all CK18 fragments that contain full-length epitopes of the protein released from both necrotic and apoptotic cells.8, 10 In cancer patients, serum M30 and M65 antigens were stable for 2 years when stored at −80°C.11 These biomarkers can be used clinically as diagnostic and prognostic factors of cancer and to predict the outcome of anticancer therapies. The biomarkers are increasingly being used in trials of new anticancer therapies. The prognostic significance of both the M30 and M65 assays has been evaluated, and it was found that the M30 and M65 assays could be important prognostic and predictive markers in several malignancies.12, 13, 14, 15, 16, 17
However, the serum levels of M30 and M65 have not been evaluated in RCC in previous studies. In the current study, we aimed to compare M30 and M65 levels in matched healthy patients with metastatic RCC, and determine the prognostic value of serum M30 and M65 levels in metastatic RCC patients.
Section snippets
Patients and Methods
This prospective study included 39 consecutive patients with histologically confirmed RCC that were followed by the Department of Medical Oncology at Istanbul University Oncology Institute. All patients were staged as metastatic according to the American Joint Committee on Cancer tumor-nodes-metastases staging classification for kidney cancer. The inclusion criteria were metastatic RCC, measurable disease, no previous systemic therapy, no previous history of cancer (except basal cell carcinoma
Patient Characteristics
Thirty-nine patients with metastatic RCC and 39 healthy control subjects were analyzed. Twenty-four patients (61.5%) were male and 15 (38.5%) were female, with a median age of 60 years (range = 45-80 years). Metastasectomy of the lung and retroperitoneal areas was carried out in 9 patients (23%). Based on the Memorial Sloan-Kettering Cancer Center (MSKCC) risk group evaluation, 84.6% of patients were in the intermediate or poor risk group. The most frequent sites of metastases were the lung (n
Discussion
In this study, serum M65 levels in patients with RCC were significantly higher than in healthy control subjects, but this was not true for M30 levels. Our results indicate that patients with elevated serum M65 levels have worse PFS compared with patients with low M65 levels. Until now, the significance of M30 and M65 levels in RCC has not been investigated. Moreover, we detected that the serum M65 level was related to poor PFS by univariate analysis, but we could not confirm these results by
Conclusion
Our results indicate that serum M65 levels are significantly higher in patients with advanced RCC than in healthy control subjects. Univariate analysis showed that elevated serum M65 was related to PFS, but the significance was not confirmed on multivariate analysis. High M65 levels might be a more reliable reflector of aggressive behaviour of cancer cells in RCC when compared with M30. Future prospective studies with larger sample sizes are needed to address the possible effect of M30 and M65
Disclosure
The authors have stated that they have no conflicts of interest.
Acknowledgments
The authors thank all of our patients and their families for their participation in this study, and the investigators and staff from the participating sites. No financial support was received for this work.
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