Peyronie’s disease (PD) is a connective tissue disorder characterized by fibrous scar tissue, known as plaque, within the tunica albuginea of the penis. This inelastic plaque prevents stretching during an erection, resulting in abnormal curvature, indentation, or shortening. The condition can cause pain, difficulty with sexual intercourse, and significant emotional distress. In 2013, the U.S. Food and Drug Administration (FDA) approved collagenase clostridium histolyticum (CCH), marketed as Xiaflex, as the first non-surgical injectable treatment for PD. Xiaflex is indicated for men with a palpable plaque and a penile curvature deformity of at least 30 degrees.
Defining Treatment Goals for Peyronie’s Disease
Determining treatment success requires defining what a successful outcome means, which is not a simple binary measure of “cure.” The primary goal is to improve both the physical deformity and the psychological impact of the condition. Success is measured using two distinct, co-primary endpoints established during clinical trials.
The first metric is the objective physical change: the reduction in penile curvature, measured in degrees. Physicians assess the degree of curvature using standardized methods, such as an erect photo or measurement during a pharmacologically induced erection. Success is often defined as achieving a specific threshold of improvement, rather than complete straightening.
The second metric is the patient’s subjective experience, quantified by the Peyronie’s Disease Questionnaire (PDQ). This tool measures the patient-reported “bother,” or the psychological and emotional distress related to the deformity and impact on sexual function. A meaningful reduction in the PDQ bother score is considered a significant part of treatment success.
Achieving a substantial reduction in both curvature and bother is the accepted standard for a positive response. This dual focus recognizes that the ultimate goal is to improve the patient’s overall quality of life and sexual function. In clinical practice, a positive response is typically defined as a 20% or greater reduction in the angle of curvature.
Analyzing Clinical Success Rates of Xiaflex
The quantitative success rates for Xiaflex were established through the pivotal Phase 3 clinical trials, IMPRESS I and IMPRESS II. These randomized, double-blind, placebo-controlled studies included 832 men with curvature deformities ranging from 30 to 90 degrees. These trials provide the most detailed data on the expected efficacy of the treatment.
In the IMPRESS trials, Xiaflex treatment resulted in a mean improvement in penile curvature of 34% compared to the placebo group. This translates to an average reduction of approximately 17 degrees in the angle of curvature. This mean improvement highlights the overall effect of the drug across the treated population.
A specific benchmark focuses on the percentage of patients who achieved a clinically meaningful improvement. In the IMPRESS trials, 56% of patients achieved a 20% or greater reduction in the curvature angle, alongside an improvement in the symptom bother domain of the PDQ. Another analysis suggests that 75% of men experienced at least a 25% improvement in the magnitude of their curvature.
Real-world use analysis showed similar effectiveness, with a 30.1% average improvement from baseline curvature. This data found that 68.7% of men achieved a 20% or greater improvement in their curvature. Furthermore, 74.4% of men who completed the full four cycles experienced a 20% or greater improvement, demonstrating the benefit of completing the full protocol.
The improvement in physical deformity was matched by a significant reduction in patient-reported symptoms. Patients receiving Xiaflex reported a greater reduction in their bother scores compared to those on the placebo. The data confirms that physical changes translated to a better perceived quality of life and reduced emotional distress.
The Xiaflex Treatment Protocol
The clinical success rates are tied to the precise, multi-step Xiaflex treatment protocol, which demands commitment from both the physician and the patient. The full course consists of a maximum of four treatment cycles, with each cycle spanning approximately six weeks. This structure means the entire regimen takes about 24 weeks to complete.
Each six-week cycle involves two distinct injection sessions, separated by 24 to 72 hours, where the physician administers Xiaflex directly into the collagen plaque. The drug enzymatically degrades the primary structural protein that forms the scar tissue, initiating physical breakdown. Following the second injection, a step known as penile modeling is performed by the physician.
The physician-performed modeling involves physically manipulating and stretching the penis to mechanically disrupt the softened plaque and reduce the curvature. This procedure is typically carried out one to three days after the second injection. The patient must continue with daily, gentle, at-home modeling and stretching exercises until the next treatment cycle begins.
The combination of the enzyme injection, physician-led modeling, and patient home exercises is necessary to achieve the reported clinical outcomes. The treatment relies on the chemical breakdown of collagen followed by mechanical force to remodel the penile tissue. After the first cycle, the physician and patient assess progress and decide whether to proceed with up to three additional cycles based on results and tolerability.
Factors Influencing Individual Outcomes
Despite the strong average success rates, individual results with Xiaflex therapy vary significantly based on patient and disease characteristics. One important factor is the stage of the disease, as Xiaflex is only indicated for men in the chronic phase. In this phase, the plaque has stabilized and there is no longer active inflammation or pain.
The initial severity of the curvature also plays a role in relative improvement. While Xiaflex is used for curvatures between 30 and 90 degrees, patients with less severe initial angles may experience a greater relative reduction. However, a significant reduction in degrees remains possible even for men with pronounced curvature.
Patient adherence to the required regimen is a major determinant of success. The process requires diligent performance of the daily at-home modeling and stretching exercises for the full duration of the treatment cycles. Non-adherent men are less likely to achieve the maximal benefit, as success relies heavily on this mechanical component.
The number of cycles a patient completes is a strong predictor of final improvement, as multiple cycles provide cumulative benefit. Men who discontinue treatment early, often due to side effects or a perceived lack of early efficacy, may not achieve the same level of curvature reduction. This highlights the importance of persisting through all four recommended cycles.