Prostate cancer is one of the most commonly diagnosed cancers among men. While treatment options have expanded, the fear of the cancer returning remains a primary concern for patients. High-Intensity Focused Ultrasound (HIFU) is a minimally invasive method used to treat localized disease, balancing effective cancer control with quality of life preservation. Understanding the surveillance methods and variables that influence the probability of recurrence is necessary for anyone considering this specialized treatment.
The Role of HIFU in Prostate Cancer Treatment
HIFU is a non-surgical, minimally invasive procedure that uses highly focused ultrasonic waves to treat cancerous tissue within the prostate. A probe inserted into the rectum delivers these sound waves, concentrating them at a specific focal point. This rapidly heats the target tissue to temperatures exceeding 140°F (60°C). This intense heat causes coagulation necrosis, destroying the cancerous cells without requiring external incisions.
HIFU is often applied as a focal therapy, meaning only the known tumor or a portion of the gland is treated, rather than the entire prostate. This approach aims to minimize common side effects like urinary incontinence and erectile dysfunction, which are associated with whole-gland treatments. Treating only part of the gland introduces a specific risk: recurrence can occur either within the treated area (in-field) or in an untreated portion of the prostate (out-field).
Detecting Recurrence After HIFU
Surveillance after HIFU relies heavily on monitoring prostate-specific antigen (PSA) levels, a process known as PSA kinetics. Unlike radical prostatectomy, where success is defined by an undetectable PSA, HIFU leaves healthy prostate tissue that continues to produce PSA. Therefore, the definition of biochemical failure—the initial sign of potential recurrence—must use a different threshold.
A PSA value that rapidly rises after reaching its lowest point, or nadir, strongly indicates treatment failure. Several definitions exist, including the Stuttgart definition, which defines biochemical failure as a PSA level rising to 1.2 ng/mL above the post-treatment nadir. Other criteria, such as the Phoenix definition (PSA nadir + 2 ng/mL), are also used. A low PSA nadir, such as below 0.2 ng/mL, is associated with lower treatment failure rates.
A rising PSA level necessitates further diagnostic steps to confirm local recurrence. Multiparametric Magnetic Resonance Imaging (mpMRI) is used to locate suspicious lesions within the remaining prostatic tissue. If the mpMRI identifies an area of concern, a targeted, or “fusion,” biopsy is performed. This procedure uses the MRI images to guide the biopsy needle directly to the suspect tissue for confirmation of cancer cells.
Risk Factors and Likelihood of Recurrence
The chances of recurrence after HIFU depend highly on the initial characteristics of the cancer and the procedure type. Patients with low-risk or favorable intermediate-risk disease are the most ideal candidates and experience the lowest recurrence rates. Conversely, patients presenting with high-risk features, such as a high Gleason score (Grade Group 3 or higher) or a high pre-HIFU PSA level (greater than 10 ng/mL), face a significantly greater likelihood of recurrence.
The probability of treatment failure correlates directly with the initial risk stratification. For example, one study found that high-risk patients experienced a failure rate of approximately 70%, compared to 8.6% for low-risk patients over a comparable follow-up period. This underscores the importance of careful patient selection for HIFU as a primary treatment.
The extent of the initial treatment also influences the risk profile, particularly the difference between focal and whole-gland ablation. Focal HIFU, which treats only the known lesion, carries the inherent risk that an undetected, clinically significant tumor may be present in an untreated area of the gland. Therefore, the technical success of the initial procedure, including achieving adequate ablation margins, is paramount to minimizing local recurrence.
Salvage Treatment Options
If recurrence is confirmed and deemed clinically significant, several salvage treatments are available, depending on the location and extent of the returning cancer. For localized recurrence, especially in a previously untreated area, a repeat focal therapy, such as a second HIFU session or cryotherapy, is often considered. These options are favored because they maintain minimal invasiveness and reduced side effects compared to whole-gland approaches.
When the recurrence is more widespread or aggressive, a definitive, whole-gland treatment may be necessary. Salvage radiation therapy, using external beam radiation or brachytherapy, is an effective option following HIFU failure. For some patients, the most aggressive approach is a salvage radical prostatectomy, which involves surgically removing the entire prostate.
Performing radical surgery after HIFU can be technically challenging due to tissue changes and scarring from the initial thermal ablation. Consequently, salvage prostatectomy carries a higher risk of complications, such as urinary incontinence and rectal injury, compared to a primary surgery. If the cancer has spread outside the prostate, systemic treatments like hormone therapy may be introduced.