Prostate cancer severity depends highly on how far the cancer has spread from its origin. When the disease extends beyond the prostate capsule, it is categorized as locally advanced, significantly changing the prognosis and treatment strategy. Seminal Vesicle Invasion (SVI) is a primary marker of this advancement, indicating cancer cells have breached the prostate’s boundaries and infiltrated adjacent reproductive structures. Understanding SVI is fundamental for determining the disease extent and guiding necessary multi-modal therapies.
Defining Seminal Vesicle Invasion
The seminal vesicles are small, sac-like glands situated behind the prostate and bladder. They produce a significant portion of semen fluid and are anatomically close to the prostate’s base, making them a common pathway for cancer spread. Seminal Vesicle Invasion (SVI) is defined by the pathological finding of prostate cancer cells within or beyond the muscular wall of one or both glands.
SVI is typically confirmed by a pathologist examining the removed prostate and seminal vesicles after a radical prostatectomy. The presence of SVI immediately classifies the disease as locally advanced, designated as pathologic T3b (pT3b) in the TNM staging system. This T3b classification distinguishes SVI from T3a disease, which involves cancer extension outside the prostate capsule but not into the seminal vesicles.
Cancer usually invades the seminal vesicles by direct extension from the prostate base or along the ejaculatory ducts. Regardless of the exact pathway, SVI indicates that the cancer has escaped its primary organ, which increases the likelihood of microscopic spread to distant sites.
The Prognostic Significance of SVI
Seminal Vesicle Invasion is a significant indicator of unfavorable outcomes, placing the disease into a higher-risk category. SVI is associated with a significantly increased risk of biochemical recurrence (BCR), defined by a measurable rise in Prostate-Specific Antigen (PSA) after definitive treatment. For patients undergoing radical prostatectomy, five-year BCR-free survival rates vary widely depending on other disease characteristics.
The severity of SVI depends heavily on associated risk factors, such as the Gleason score and the extent of invasion. High-grade disease combined with SVI results in a poorer prognosis than SVI alone. The extent of invasion also matters; cancer extending to the distal part of the seminal vesicles carries a higher risk of progression than invasion limited to the part closest to the prostate.
SVI often signals a larger, more aggressive tumor burden. Prognosis also differs based on laterality: bilateral involvement (both seminal vesicles) shows significantly lower rates of recurrence-free survival compared to unilateral involvement. These factors determine the overall risk stratification and the necessary intensity of the treatment plan.
Tailored Treatment Approaches for SVI
Since Seminal Vesicle Invasion signifies locally advanced, higher-risk disease, treatment strategies must move beyond single-modality approaches. Management typically involves a multi-modal combination of surgery, radiation, and hormonal therapy. This shift is necessary because SVI elevates the risk of cancer cells having already traveled outside the immediate surgical field.
One primary approach is Radical Prostatectomy, removing the entire prostate and seminal vesicles. Following surgery, patients with SVI often require adjuvant therapy delivered immediately to reduce recurrence risk. This adjuvant treatment usually consists of external beam radiation therapy to the surgical bed, combined with a course of Androgen Deprivation Therapy (ADT). ADT, or hormonal therapy, reduces male hormones that fuel prostate cancer growth, helping eliminate microscopic cancer cells.
Alternatively, primary treatment may involve high-dose Radiation Therapy combined with long-term ADT, bypassing initial surgery. The radiation field covers the prostate, seminal vesicles, and sometimes the pelvic lymph nodes for comprehensive coverage. Long-term ADT, often lasting 18 to 36 months or more, is integrated with radiation to enhance effectiveness against the aggressive nature of SVI.
Long-Term Monitoring and Recurrence Management
Patients with SVI require continuous monitoring long after initial multi-modal treatment due to the elevated risk of recurrence. The standard surveillance method is the regular measurement of Prostate-Specific Antigen (PSA) levels. PSA testing frequency is generally every three months for the first few years, with the specific recurrence threshold depending on the initial treatment.
For patients who underwent radical prostatectomy, biochemical recurrence is typically defined as a confirmed PSA level of 0.2 ng/mL or higher. Following radiation, the definition is usually a PSA rise of 2.0 ng/mL above the lowest value achieved after therapy. If recurrence is detected, physicians often proceed with salvage therapies to attempt long-term control.
Salvage radiation therapy to the prostate bed is common for recurrence after surgery, especially if the PSA rise is slow and distant spread is absent. For patients with a rapid PSA rise or evidence of distant spread, systemic therapies, including advanced hormonal agents or chemotherapy, are used. The goal is to catch any reappearance early, ensuring timely secondary treatments to maintain disease control.