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TMPRSS2 - ERG Loci Abnormality in Salvage Radiation Therapy (sRT) Refractory Prostate Cancer Patients

2011-10-01 20:24:46

International Journal of Radiation Oncology; 2011 Oct; 81(2):S761


R. Hannan, J. Shan, S. Gandhi, K. Bernstein, D. Blakaj, C. Montagna, T. Tong, S. Kalnicki, M. Garg, C.
Guha



Abstract



Purpose/Objective(s):



TMPRSS2-ETS translocation has been identified in greater than 50% of prostate cancer patients and has been associated with a more aggressive molecular subtype of prostate cancer. In a highly resistant cohort of prostate cancer patients that have failed both radical prostatectomy (RP) and sRT, we screened for abnormalities in the ERG and TMPRSS2 loci in prostatectomy tissue sections using a dual-color break-apart fluorescence in situ hybridization (FISH) assay.



Materials/Methods:



In this IRB approved study, paraffin embedded prostatectomy tissue slides from seven consecutive sRT patients with biochemical recurrence (BR) of prostate cancer were obtained. Slides were incubated overnight on a slide warmer at 60°C, de-paraffinized by immersing in CitriSolv for 3x10 minutes (m) at room
temperature, dehydrated in 100% ethanol at room temperature and allowed to air dry. The slides were then treated with pretreatment buffer (Paraffin Pretreatment Reagent Kit, Abbott Molecular, IL) at 80°C for 30m, protease solution at 37°C for 30m, followed by washing and successive dehydration in 70%, 90% and 100% ethanol. Fluorophore labeled ERG (RP11-24A11 and RP11-372O17) and TMPRSS2 (RP11-662D5 and RP11-260O11) probes (Empire Genomics, NY) were denatured on ThermoBrite (Abbott molecular, IL) at 76°C for 5m. Slides were then incubated with the probes in a humidified chamber at 37°C for at 16h. After extensive washing (2xSSC with 0.3% Tween 20), air drying slides were analyzed with DAPI in ZEISS Axiovert 200 microscope (mag. 10x63).



Results:



Patients analyzed were in the intermediate risk group with Gleason score of 7 or 8, median pre-treatment PSA of 8.2 (range 3-26) and pathologic stage between T2c-T3b. All patients exhibited at least one high-risk feature of positive margin, seminal vesicle invasion, extra-capsular extension, peri-neural invasion or high volume disease. Median time to BR after RP was 11.5 months (6.7-55.4). sRT was 66.6Gy IMRT to the prostatic bed. Median time to BR after sRT was 9.4 months (5-30.4). FISH analysis showed chromosomal abnormalities of insertion, deletion, translocation or amplification in either ERG or TMPRSS2 locus in six out of seven patients. Abnormality in ERG was found in 4 patients and TMPRSS2 was found in 5 patients. Indirect evidence for TMPRSS2:ERG fusion was noted in 4 of the seven patients.



Conclusions:



Increased frequency of chromosomal rearrangement in the ERG and TMPRSS2 loci in this cohort of highly treatment resistant patients suggest a key role for these genes in the aggressive nature and radioresistance of prostate cancer. The data warrants a closer examination of the mechanism of action and clinical implication of these loci in a prospective manner. A larger cohort of patients is currently undergoing analysis.



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