Prostate cancer treatment depends largely on how far the disease has progressed. Seminal Vesicle Invasion (SVI) immediately classifies the disease as locally advanced and high-risk. SVI indicates that the cancer has broken through the prostate’s outer boundary and extended into the adjacent seminal vesicles. This advanced local spread necessitates a more aggressive, multi-faceted treatment plan. Management of prostate cancer with SVI involves complex decisions between surgery and radiation-based approaches, often combining different therapies to maximize the chance of a successful outcome.
Significance of Seminal Vesicle Invasion
Seminal vesicle invasion directly impacts the staging and prognosis of prostate cancer. When cancer has invaded the seminal vesicles, it is classified as pathological stage pT3b according to the Tumor, Node, Metastasis (TNM) staging system. This designation means the disease has progressed beyond the confines of the prostate gland, indicating a higher volume of cancer and a greater likelihood of microscopic spread.
The presence of SVI is an adverse prognostic factor, consistently associated with a higher risk of cancer returning, specifically as biochemical recurrence. Invasion into the muscular wall of the seminal vesicle, rather than just the surrounding tissue, is the precise pathological definition of SVI. This finding signals that standard treatments for localized disease are insufficient, requiring intensified therapy.
Primary Surgical Strategy
Radical Prostatectomy (RP), the surgical removal of the prostate and seminal vesicles, is a viable option for select patients with SVI. The goal of surgery is to completely remove all visible cancer and offer immediate pathological staging. Because of the high risk of microscopic spread, RP is almost always accompanied by an extended pelvic lymph node dissection (ePLND).
The ePLND involves removing lymph nodes from a wider area, including the external iliac, obturator, and internal iliac nodes, which are common sites for initial cancer spread. This extended removal is performed because SVI carries a high risk of lymph node involvement and provides the most accurate staging information. For many patients with SVI, surgery alone is insufficient to achieve long-term control. Post-operative findings, such as positive surgical margins or detectable post-operative Prostate-Specific Antigen (PSA) levels, often lead to subsequent “adjuvant” or “salvage” treatment, typically involving radiation and/or hormone therapy.
Radiotherapy and Systemic Therapy Protocols
The standard non-surgical approach for prostate cancer with SVI relies on External Beam Radiation Therapy (EBRT) combined with Androgen Deprivation Therapy (ADT). This multimodal strategy is the most common definitive treatment for pT3b disease. The EBRT delivers high-energy radiation beams to the prostate and the entire volume of the seminal vesicles, ensuring the entire area of known disease is treated.
Modern techniques, such as Intensity-Modulated Radiation Therapy (IMRT), precisely shape the radiation dose around the target area, maximizing the dose to the cancer while reducing exposure to nearby organs like the bladder and rectum. The systemic component, ADT (hormone therapy), is administered concurrently to inhibit the production of testosterone, the primary fuel for prostate cancer growth. ADT works by shrinking the tumor and making cancer cells more susceptible to radiation.
For SVI, ADT is typically given for an extended duration, often ranging from 18 to 36 months, in combination with radiation. Studies show that this longer duration of hormone suppression, compared to shorter courses, is associated with significantly better outcomes, including improved metastasis-free and overall survival rates. The addition of newer, more potent hormonal agents is also being investigated to improve long-term control.
Patient and Disease Characteristics Guiding Selection
The decision between a primary surgical approach and a primary radiotherapy/systemic therapy approach for SVI is individualized and rests on patient and disease-specific factors. A patient’s overall health and the presence of other medical conditions influence the choice, as major surgery may be poorly tolerated by those with significant comorbidities. Age, life expectancy, and the patient’s preference regarding potential side effects are also considered.
Disease characteristics, such as the initial PSA level, the Gleason score (which measures cancer aggressiveness), and the extent of SVI seen on imaging, help predict the likelihood of success for either approach. Patients with a lower burden of disease may be better candidates for surgery, while those with a very aggressive presentation often benefit from the definitive, multi-year systemic control offered by the radiation and ADT protocol. Ultimately, selection involves a detailed discussion between the patient and a multidisciplinary team, weighing long-term cancer control against the impact on quality of life.