When prostate cancer grows beyond the prostate gland and into the seminal vesicles, it is referred to as having seminal vesicle invasion (SVI). The seminal vesicles are a pair of glands located just behind the prostate that contribute fluid to semen. This condition is a form of locally advanced prostate cancer, meaning the cancer has moved into adjacent tissues but has not yet spread to distant parts of the body. This type of cancer is more advanced than a tumor confined solely to the prostate, but it is not considered metastatic.
Understanding Diagnosis and Staging
The identification of seminal vesicle invasion relies on several diagnostic tools to determine the extent of the cancer. A digital rectal exam (DRE) may allow a physician to feel if the tumor has grown beyond the prostate’s edge. However, advanced imaging provides a much clearer picture, and a multi-parametric Magnetic Resonance Imaging (mp-MRI) scan of the prostate is highly effective at visualizing the seminal vesicles and detecting tumor infiltration.
A definitive diagnosis is confirmed through a prostate biopsy. If cancer cells are found in tissue taken from the area where the seminal vesicles join the prostate, it confirms invasion. This finding is fundamental to the staging process, which classifies the cancer’s progression. The presence of seminal vesicle invasion specifically classifies the tumor as stage T3b under the TNM (Tumor, Node, Metastasis) system.
This T3b designation is a factor in medical decision-making because it indicates that the cancer is no longer confined within the prostate capsule. This stage is associated with a higher risk of recurrence compared to organ-confined disease. Therefore, the staging process directly informs the intensity and type of treatment recommended by the oncology team.
Combined Radiation and Hormone Therapy
The most common treatment for prostate cancer with seminal vesicle invasion is a combination of external beam radiation therapy (EBRT) and androgen deprivation therapy (ADT), also known as hormone therapy. The standard protocol involves a long course of ADT, often starting before radiation begins and continuing for a total of 18 to 36 months. This extended duration is based on clinical trials showing improved outcomes for men with high-risk, locally advanced disease.
EBRT uses targeted, high-energy X-rays to destroy cancer cells. Modern techniques like intensity-modulated radiation therapy (IMRT) allow for high doses of radiation to be delivered directly to the prostate and the invaded seminal vesicles while minimizing exposure to surrounding healthy tissues. The treatment is typically delivered in daily sessions over several weeks.
Prostate cancer cells use testosterone, a primary male hormone or androgen, as fuel for growth. ADT works by drastically reducing the body’s testosterone levels, which can slow the cancer’s growth, shrink the tumor, and may eliminate microscopic cancer cells. This hormonal suppression also makes the remaining cancer cells more vulnerable to the cell-killing effects of radiation.
Patients undergoing this combination therapy may experience side effects from both treatments. ADT commonly causes side effects related to low testosterone, including:
- Hot flashes
- Fatigue
- Loss of libido
- Potential loss of bone density and muscle mass over the long term
Radiation therapy’s side effects are localized to the pelvic region and can include urinary issues, such as increased frequency or urgency, and bowel problems like diarrhea or rectal irritation.
The Role of Radical Prostatectomy
Surgery, in the form of a radical prostatectomy, is another treatment path, though it is less frequently used as the primary approach for prostate cancer with known seminal vesicle invasion. The procedure involves the complete surgical removal of the prostate gland, both seminal vesicles, and often, a selection of nearby pelvic lymph nodes to check for any further spread.
Surgery alone is rarely sufficient to control T3b disease, as the invasion of the seminal vesicles indicates a high probability that cancer cells have escaped the surgical area. Consequently, patients who opt for a radical prostatectomy almost always require additional treatments, known as adjuvant therapies, to reduce the risk of the cancer returning.
These follow-up treatments typically include radiation therapy to the prostate bed (the area where the prostate was) and often a course of hormone therapy. The decision to pursue surgery depends on various factors, including the patient’s age, overall health, and the specific characteristics of the tumor. The potential side effects of radical prostatectomy are significant and include a high risk of urinary incontinence (leakage) and erectile dysfunction.
Post-Treatment Monitoring and Follow-Up
After completing primary treatment, a structured long-term follow-up plan is put in place. The central tool for this surveillance is the regular measurement of the prostate-specific antigen (PSA) level in the blood. PSA tests are typically performed every few months for the first few years and then at longer intervals.
A consistent rise in PSA levels after treatment is known as a biochemical recurrence. The specific definition of biochemical recurrence depends on the initial treatment. After a radical prostatectomy, recurrence is defined as a PSA level rising to 0.2 ng/mL or higher. Following radiation therapy, it is defined as a rise of 2.0 ng/mL above the lowest point the PSA reached (the nadir).
Detecting a biochemical recurrence does not mean that the cancer has become widespread or is causing symptoms. Depending on how quickly the PSA is rising and other individual health factors, doctors may recommend additional imaging, such as a PSMA-PET scan, to locate the source of the recurrence. This information helps determine if and when subsequent treatments, often called salvage therapies, are needed.