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I have recently heard from many new friends here and on some patient forums with concerns about seminal vesicle involvement by prostate cancer.  Often times, when giving a patient his pathology result after a prostatectomy, the urologist will mention the seminal vesicle but not explain its significance or, more importantly, the significance of involvement of the seminal vesicle by prostate cancer.  In this post, I want to shed some light on what the seminal vesicles are, why it is important to know if prostate cancer invades them, and what can be done once seminal vesicle involvement is determined after a prostatectomy.

 The Seminal Vesicle Exposed

A good place to start this discussion is to provide a little background about the seminal vesicle.  As its name implies, the seminal vesicle is basically a container for semen.  Two such seminal vesicles are located behind the prostate.  On diagrams, they look like bunny ears emerging behind the prostate and the bladder.  The seminal vesicles, along with the prostate, produce most (about 90%) of the semen released during ejaculation.  They are attached to the prostate and actually have ducts which empty into the center of the prostate.  This is the part of the prostate through which the urethra travels into the bladder (the “donut hole”).  These ducts connect to those of the tubes carrying sperm from the testes (the vasa differentia).  When ejaculation occurs, the sperm from the vasa differentia mix with the semen produced by the seminal vesicles and the prostate in the part of the urethra travelling through the prostate. The whole mixture is then propelled out through the urethra and penis by means of a forceful contraction of the muscles of the pelvis (this contraction is what provides the feeling of an orgasm).  As is probably clear from this description, the seminal vesicles are intimately associated with the prostate. As a result, prostate cancer that has escaped the prostate can proceed to directly invade the seminal vesicles.

Prostate cancer invades the seminal vesicles in about 3-7% of men with the disease.  Historically, invasion of the seminal vesicle by prostate cancer has been considered a sign of a very poor prognosis for men with prostate cancer.  In the past, studies reported that 50% of men with seminal vesicle invasion actually had metastatic disease at the time of surgery and, in fact, invasion of the seminal vesicle, itself, has been considered metastatic disease by many urologists.  This idea was supported by the fact that the majority of patients with seminal vesicle invasion demonstrated a rather quick biochemical recurrence after prostatectomy. This rapid recurrence of PSA after prostatectomy often led to subsequent documented metastatic disease.  As a result, the survival rate for men with seminal vesicle invasion was historically reported to be as low as only 32% at 7 years. 

With the era of PSA testing, outcomes for men with prostate cancer invading the seminal vesicles have been somewhat more encouraging.  The chance of a PSA recurrence within 10 years of prostatectomy remains very high (around 80%) for men found to have seminal vesicle invasion.  The rate of metastatic disease, as well, remains high at 44% for these men at 10 years after surgery.  However, these high rates of recurrence and metastasis do not appear to the lead to the dismal survival rates I previously mentioned.  In fact, recent studies demonstrated that at 10 years after surgery, men with invasion of the seminal vesicles demonstrated an overall survival rate of 61%.  In addition, a cancer specific survival rate of 84% has been described for these men.  That statistic is pretty astounding if you think about it: despite extremely high recurrence and metastasis rates, only about 16% of men with seminal vesicle invasion died of prostate cancer at 10 years after surgery!  This discrepancy is most likely a strong testament to the efficacy of hormonal therapy in managing metastatic disease.

Because of the high rates of metastatic disease and poor prognosis associated with seminal vesicle invasion, patients with this finding have often been treated as if they had metastatic disease.  As a result, doctors have waited for early signs of a PSA recurrence after which they initiated hormonal therapy to manage impending metastatic disease.  Even with such a pessimistic, conservative approach, the impressive 10 year cancer specific survival of 84% mentioned above was attained for men with seminal vesicle invasion at 10 years after surgery.

Recently, however, a new, viable treatment option has become available for men with seminal vesicle invasion thanks to a randomized trial published in 2008.  The SWOG 8794 trial included 139 men that were found to have seminal vesicle invasion with or without positive margins or extracapsular extension (I cover both of these topics in prior posts).  These men were randomized into 1 of 2 treatment arms:

1)    Adjuvant Radiation Therapy

2)    Observation

Of note, men in the observation arm of the study could be treated at the digression of their physicians once a recurrence was documented.  This treatment could include either delayed radiation or hormonal therapy. 

The study demonstrated that men undergoing adjuvant radiation therapy enjoyed a significantly higher freedom from recurrent disease of 36% versus 12% for those in the observation arm.  In addition, men undergoing the radiation therapy appeared to be half as likely to need long term hormonal therapy as those in the observation arm.  The study also found that, after 10 years of follow up, men undergoing adjuvant radiation therapy enjoyed a higher rate of freedom from metastasis (66% versus 47%) and a higher overall survival rate (71% versus 51%) as compared to those men undergoing observation and possible delayed treatment.  The differences in freedom from metastasis and in overall survival, although impressive, were not statistically significant.  This lack of statistical significance is most likely due to the 10 year follow up of the study, the small overall number of patients, and the fact that men in the observation arm did receive hormonal therapy or salvage radiation therapy. Nonetheless, the results of the study are clinically significant and have really changed the approach to managing prostate cancer in men with seminal vesicle involvement. Rather than waiting for recurrent cancer and palliatively treating metastatic disease, many doctors are now aggressively treating men with seminal vesicle disease with adjuvant radiation therapy.  While the side effects of radiation need to be kept in mind, the potential benefit of this adjuvant radiation therapy appears to be substantial.  Another fact important to point out is that the dose of radiation administered to patients in this study was fairly modest as compared to that received by contemporary patients.  As such, one would imagine that the results of the study would be even more impressive if current radiation doses were used.

Invasion of the seminal vesicle is usually a sign of an aggressive cancer, very different from the “run of the mill” Gleason 6, localized disease usually thought of when referring to prostate cancer.  Seminal vesicle involvement is a poor prognostic indicator associated with high rates of recurrence and metastatic spread.  In the PSA era, however, seminal vesicle involvement no longer appears to be the death sentence it was historically thought to be.  Aggressive management with adjuvant radiation can delay prostate cancer recurrence and spread.  In addition, the prudent use of hormonal therapy to manage metastatic disease can lead to many more years of life.  Overall, while certainly a serious condition to deal with, seminal vesicle invasion can still be successfully treated when encountered in men with prostate cancer.