How Do We Know the Cancer is Cured

Some people think that with radiation therapy we are trying to do some sort of minimal treatment so that we can put off big guns like surgery for a few years.  This is simply false.  The goal of CyberKnife is to cure the cancer.  Permanently.   Completely.  I.e so that it never ever comes back in your lifetime.  The goal is not to “buy you more time”.

So how do we prove the cancer is gone after CyberKnife?

There is saying that you cannot prove a negative.  If you do a biopsy after the CyberKnife is completed, even if the biopsy is negative (normal) there still can be cancer cells lurking in areas of the prostate gland that the biopsy needles did not reach.   This is called a false negative.   A negative biopsy does not prove there is no cancer, but it is still an encouraging result to see.

Confusingly, if you do a biopsy in the first 24 months after radiation and it still shows cancer cells, these actually may be terminally injured cancer cells that are destined to die.   This is called a false positive.  So, we try to avoid doing repeat biopsies in the first 2 years after CyberKnife, and we also avoid doing biopsies to “prove” that the cancer is cured.

We can never be 100% that your prostate cancer is cured.  But once your PSA drops down to less than 1.0, the longer it stays low and stable the higher the probability that you have been cured.  For example, if it is 10 years post-CyberKnife, and your PSA is at 0.1, there is probably a 99% chance it is permanently cured, I.e that it will never recur during your life.

This is confusing to many people, that although we think the cancer is cured we cannot be certain.   Cancer staging, chance of success, and risk of side effects unfortunately always involves probabilities and statistics, and are never absolute certainty.  Like the rest of life.

Monitoring the PSA After Treatment

The main way we follow prostate cancer after radiation is with PSA blood testing every 3 – 6 months.

After radiation, the PSA can take 5 years to reach its lowest level.

The PSA may bottom-out at anywhere from 0.1 to 2.0 by the 5 year mark.  Remember that below 4.0 is the cutoff for a normal PSA for the general population who have never had prostate cancer, so these values are well within the “normal” range.  I typically tell my patients that below 1.0 is the new normal after radiation therapy, but that it can take a few years to get down below that level.   In fact, usually the PSA drops down to less than 0.5, and in most studies the average PSA at the 5 year mark after CyberKnife was 0.1.

The other thing to know about PSA during the monitoring process is that even if the cancer is cured the PSA can fluctuate and bounce up and down sometimes.   If the PSA rises the first thing to do is to be patient and test it again in 3 months.  It will usually drop back down.

Little rises in the PSA are not a big deal.  However, if the PSA rises to over 2 points above its all-time minimum, this may be a recurrence.  In addition, if the PSA rises on 3 consecutive readings (which are done at least a couple months apart) this may also possibly be a recurrence.

A few basic rules for PSA and monitoring prostate cancer after treatment

• PSA is found only in men.
• PSA comes from both healthy prostate cells and from prostate cancer cells.
• PSA levels can go up and down day to day in the general population.
• A normal PSA in the general population is considered less than 4.0, although there are different normal ranges for different ages.
• Prostate cancer cells that are anywhere in the body will make the PSA level rise.
• If the prostate has been surgically removed the PSA should be 0, basically undetectable or less than 0.1. Levels above that must mean that there are prostate cancer cells somewhere in the body.
• Super-sensitive PSA tests just give you more digits after the decimal point. A PSA of 2 or 2.2 or 2.23 or 2.227 are all basically the same.
• PSA’s may bounce up and down after radiation treatment. It is the trend we look for.
• Don’t panic if the PSA rises. Wait 3 months and check again.
• A normal PSA after radiation is typically less than 1.0, i.e. “Zero point something”, but there is no strict cut off.
• I like to see the PSA to drop below 1.0 within 2 years of radiation, but again there is no strict cut off.
• It can take 5 years or longer for a PSA to reach its minimum value after radiation. The lowest value is called the nadir.
• PSA goes down to an average value of 0.1 five years after CyberKnife.
• The PSA can shoot up wildly after biopsy, after placement of marker seeds, if there is a prostate infection, and during radiation therapy.
• To diagnose a recurrence we look for a significant rising trend in the PSA: levels rising on three consecutive measurements done 3 months apart, or a PSA that is 2 points higher than a previous minimum (nadir) value. The definition that radiation oncologists use in studies is a rise of 2 points higher than a previous minimum.
• Occasionally, even if there is a significant rising trend in the PSA there may not be a cancer recurrence. It could be a “bounce” which is a jump in the PSA caused by prostate inflammation.   Some suspected failures turn out to be successes!

 

Follow-Up Schedule

The first PSA should be taken 3 months after the radiation is complete, to give it a chance to settle down.

After that, I recommend that a PSA level be taken every 3 – 6 months for the first 2 years.  Every 3 months if you’re the type who worries.

If the PSA is less than 1.0 at the 2 year mark and behaving well, then the PSAs can be drawn every 6 months.

After 5 years, if the PSA is very low (0.2) if can be tested every 6 – 12 months.

This schedule may be made stricter or looser depending on the risk level of the cancer.

If the PSA starts to rise or behave erratically, it should be checked every 3 months.

There is little value in checking the PSA sooner than 3 months, except in occasional cases where there is a big jump I will check it again 6 weeks later.

I like to see patients at the 3 month mark after CyberKnife, but it is not mandatory.  After that you can either come see me for the PSA’s or else get them done with your primary care doctor.

If you are receiving Lupron hormone therapy as part of your treatment program then you would return to the clinic every 3 – 4 months for a Lupron injection until the series of injections is over.  After that, I like to follow high-risk prostate cancer patients more closely to monitor for recurrence and I may recommend that you see me every 6 months for 5 years.

You don’t need to see a urologist in followup unless you are having significant urinary or sexual symptoms, and would like a urologic consultation regarding those symptoms.  We will try to manage those symptoms in the radiation oncology clinic, but we don’t have all the tools that a urologist does for these problems.