B41: Use of diffusion weighted-MRI (DW-MRI) as a biomarker of clinical outcome in muscle invasive bladder cancer (MIBC)
1The Institute of Cancer Research, London, UK,2The Royal Marsden Hospital NHS Foundation Trust, Sutton, Surrey, UK
DW-MRI quantifies water molecule motion within tissue using the apparent diffusion coefficient (ADC). As an imaging biomarker it has been related to treatment response in solid tumours. Its use as a prognostic marker in bladder cancer remains novel.
92 patients with confirmed MIBC suitable for radical treatment were recruited prospectively to an ethics approved protocol. DW-MRI was performed on a 1.5T system using b-values 0,50,100,250,500 and 750s/mm2 following trans-urethral resection of the tumour but prior to any other treatment. Tumour volume drawn on 750 s/mm2 images were transferred to the corresponding ADC map to determine mean values. Skew and kurtosis values were used to assess tumour heterogeneity. Associations between mean values were compared to progression free and overall survival.
All tumours seen on T2 weighted images were identified on DW-images. In 26 patients no tumour was seen on T2 images or DW-images. Of the 66 patients available for analysis, 47 received radical radiotherapy to the bladder, 16 received cystectomy, and 3 patients declined radical treatment following neo-adjuvant chemotherapy. After median follow-up of 22 months (range 3-127 months), 35 patients experienced disease progression, 19 had extravesical progression not amenable to subsequent radical treatment, and 29 patients had died.
Mean DW-MRI defined tumour volume was significantly greater in those experiencing extravesical progression (31.2 cm2; std.deviation 31.6cm2 vs 14.6cm2; std.deviation 21.1 cm2; p= 0.017), any progression (25.7cm2; std.deviation 29.2 cm2 vs 11.3 cm2; std.deviation 16.8cm2; p=0.019), and poor survival (24.8cm2; std.deviation 26.2cm2 vs 12.8 cm2; std.deviation 26.2cm2; p=0.049).
Tumour mean ADC value was 1.4 x10-3mm2/s (std.deviation 0.3 x10-3mm2/s range 0.9-2.5 x10-3mm2/s). Mean skew and kurtosis was 1.8 (std.deviation 1.9; range 0.2-11.8) and 10.8 (std.deviation 29.0; range 0.9-194.8) respectively. Baseline ADC, skew and kurtosis was not significantly associated with progression free or overall survival.
DW-MRI may provide prognostic information in bladder cancer but further work is needed.