Location of residual cancer after transrectal high-intensity focused ultrasound ablation for clinically localized prostate cancer

Study Type – Therapy (case series) Level of Evidence 4 What’s known on the subject ? and What does the study add? Transrectal High‐Intensity Focused Ultrasound (HIFU) ablation has been used as a minimally invasive treatment for localized prostate cancer for 15 years. Five‐year disease‐free survival rates of 66–78% have been reported, challenging the results of external‐beam radiation therapy. Usually, a 6‐mm safety margin is used in the apex to preserve the urinary sphincter and potency. The influence of this 6‐mm margin on the results of the treatment has never been assessed. This retrospective study of a cohort of 99 patients who underwent systematic biopsy 3–6 months after HIFU ablation for prostate cancer (with a 6‐mm safety margin in the apex) shows that post‐HIFU residual cancer is found more frequently in the apex. Therefore, new strategies improving the prostate destruction at the apex while preserving the urinary continence need to be found.

OBJECTIVE

? To evaluate whether the location (apex/midgland/base) of prostate cancer influences the risk of incomplete transrectal high‐intensity focused ultrasonography (HIFU) ablation.

PATIENTS AND METHODS

? We retrospectively studied 99 patients who underwent prostate cancer HIFU ablation (Ablatherm; EDAP, Vaulx‐en‐Velin, France) with a 6‐mm safety margin at the apex, and had systematic biopsies 3–6 months after treatment. ? Locations of positive pre‐ and post‐HIFU sextants were compared. ? The present study included two analyses. First, sextants negative before and positive after treatment were recoded as positive/positive, hypothesizing that cancer had been missed at pretreatment biopsy. Second, patients with such sextants were excluded.

RESULTS

? Pre‐HIFU biopsies found cancer in all patients and in 215/594 sextants (36.2%); 55 (25.6%) positive sextants were in the apex, 86 (40%) in the midgland and 74 (34.4%) in the base. ? After treatment, residual cancer was found in 36 patients (36.4%) and 50 sextants (8.4%); 30 (60%) positive sextants were in the apex, 12 (24%) in the midgland and eight (16%) in the base. ? Both statistical analyses found that the locations of the positive sextants before and after HIFU ablation were significantly different (P < 0.001), with a higher proportion of positive apical sextants after treatment. ? At the first analysis, the mean (95% confidence interval) probability for a sextant to remain positive after HIFU ablation was 8.8% (3.5–20.3%) in the base, 12.7% (5.8–25.9%) in the midgland and 41.7% (27.2–57.89%) in the apex. ? At the second analysis, these same probabilities were 5.9% (1.9–17%), 9.9% (3.9–23.2%) and 27.3% (13.7–47%), respectively.

CONCLUSION

? When a 6‐mm apical safety margin is used, residual cancer after HIFU ablation is found significantly more frequently in the apex.