The primary appeal of focal therapy is the lower risk of treatment-related complications compared with the complications experienced with whole-gland therapy. The fact that focal therapy has better functional results is not in dispute; subjecting only a portion of the prostate and periprostatic tissue to the potential harms of treatment has less overall impact on function than whole-gland therapy. Likewise, the ability to deliver ablative energy is also not in dispute, whether using high-intensity–focused ultrasound, cryotherapy, or focal laser ablation.

The main issues with the use of focal therapy revolve around the identification of focal disease and, more importantly, the definition of treatment success. Most prostate cancers are multifocal, with disease occurring throughout the prostate, although there are some patients who have an index lesion (ie, where the largest or highest-grade cancer is focal) and others who have only a single area of disease. While magnetic resonance imaging (MRI) is extremely useful for making that assessment, it is not completely accurate. Thus, focal therapy always runs the risk of undertreatment by missing areas of the disease. 

The other important issue is related to determining treatment success. Since you are not treating the entire prostate, you cannot expect the prostate-specific antigen (PSA) to become undetectable. The lower the PSA level goes, the better; however; the effect also depends on how much of the prostate was treated. Some have suggested that the PSA should, ideally, go down to less than 1 ng/mL, but that may be an unrealistic threshold for a patient who still has a sizable amount of untreated prostate tissue. 

While guidelines recommend that patients have follow-up biopsies to determine whether the focal therapy was successful, that has not been the standard in many published studies. Although patients are often understandably reluctant to have additional biopsies, follow-up biopsies should be standard practice in both the treated and untreated portions of the prostate because we know that simply following the PSA is not sufficient to recognize treatment failure. 

During this AUA2021 session, the speakers discussed the case of a middle-aged man with a PSA of 7 ng/mL, a stage T2a lesion, and a Prostate Imaging Reporting and Data System 4 lesion on MRI; important considerations were brought to the fore. Regarding the selection of patients for focal therapy, one issue that speaker Peter R. Carroll, MD, MPH, alluded to is that, unfortunately, patients who are probably better treated with active surveillance may be offered focal therapy, with the appeal based on the low morbidity and the low risk of functional side effects. 

I think that low- and very low-risk prostate cancer is best managed with active surveillance rather than with focal therapy. As part of a multimodal approach, focal therapy has the biggest potential role in the treatment of patients with small, favorable, intermediate-risk cancers that are localized to an MRI index lesion; those who are less ideal candidates for active surveillance; and those who do not want to be subjected to the potential morbidity of whole-gland therapy. However, the use of focal therapy in an effort to preserve erectile function is a double-edged sword. The preservation of erectile function may be hampered in a patient who fails focal therapy compared with a patient who uses surgery as a primary treatment. This is because it is difficult—and likely not even advisable—to perform nerve-sparing procedures on the side where focal therapy was performed.