So, Dr. Scholz, you know, there's a lot of different prostate cancer terms out
there and PSA obviously is a big topic of conversation, but there's also free PSA and
I think patients oftentimes don't really know what the difference is, so can you explain what
free PSA is and is it really relevant? Is that something patients should be paying attention to?
So, free PSA was one of the early attempts to refine the PSA test further. We're using the PSA
oftentimes in men who have already been diagnosed to gauge how bad the cancer is, but most people
are familiar with it as a screening tool in healthy men to detect prostate cancer
at an early and curable stage, but we know there's a lot of limitations; men can get prostatitis,
they can have big prostates, and recent sexual activity, all these things can elevate PSA and
create confusion about what's going on and is prostate cancer present or not.
So, one early attempt, which has been around for a long time, is something called free PSA.
Free PSA is a subtype of PSA that is made less frequently in men with big prostates,
and so since one of the confusing factors about PSA is that big prostates cause more PSA,
free PSA will help tell you which of those patients are the guys with big prostates and maybe
if they have this type of free PSA, then--which signals a big prostate--maybe the elevated PSA
isn't coming from cancer, maybe it's coming from the big prostate. It has some utility. It's
measured as a percentage of of total PSA and when the percentage of free PSA drops below, say, 9%,
that suggests that a big prostate is not present and therefore a PSA elevation is more likely to be
from prostate cancer or maybe prostatitis and maybe further investigation is necessary. I don't
look at free PSA as a modern test any longer. There are better tests such as the OPKO 4K blood
test that can give you a percentage likelihood of Gleason grade 7 or higher cancer, which is the
kind you want to know about, and so I don't order free PSAs anymore, but it does come up a lot.
People are still being tested with free PSA; it's nice to know what to do with it. Once you
have done an imaging study of the prostate, say an MRI or a color doppler, you know how
big the prostate is and free PSA is an indirect attempt to tell how big the prostate is whereas
the imaging studies give you an actual measurement and then you can go on and use something called
PSA density--the ratio of the size of the prostate to the amount of PSA--and that gives you greater
clarity as to whether the high PSA is coming from a cancer as opposed to just a big gland.
When it comes to the PSA test, then, there are multiple things that can affect
it before having your PSA test like, you know, we say don't ride a bicycle or don't have sex.
I know that one of the questions is, you know, does dehydration or hydration
change it? So what are the core things that patients should know do affect the PSA test?
So, you mentioned the ones that are most common. Hydration is not a factor;
diet is not. You don't need to be fasting. Your blood sugar doesn't affect your PSA. One thing
that people often overlook is laboratory errors. There are millions of PSAs being done every year
and sometimes the lab laboratory has a bad day and you'll just get a weird number. So, people do need
to be aware of the fact that the PSA is not cast in stone; if it's elevated, the first step for
many people should simply be to repeat it, see if it's consistently elevated. If it's just kind
of a one-time thing from as you mentioned sexual activity or bike riding or a lab error, and then
only after the PSA is confirmed to be elevated should further investigations follow up.
If they're going to retest their PSA because of an elevated number,
how soon should they do it? Like two days? Two weeks?
Yeah, they say that delay after sexual activity should be about a day or two,
so it can be repeated quite quickly if you like.
So, is a PSA that is high but stable indication that there is prostate cancer growing?
Well, people overestimate the precision of PSA, and as we've stated before, people
should look at this test more like a check engine light on the dashboard of your car
than a gauge that indicates how much cancer is present or what's going on with the cancer. When
we're staging newly diagnosed prostate cancer, we we divide PSA up to increments of 10, like 1-10,
10-20, and 20 and above, and that provides a little bit of background information as to whether
the cancer is more likely to be risky or not but it's not very precise at all. PSA is a good test
to trigger further investigations and it's a good test to see if treatment is working because
when you start--go through surgery, radiation, hormone therapy--the PSA should decline sharply,
but it's not a very accurate indication of how much cancer is present or how much it's growing.
Yeah, that's interesting because I know another patient asked, you know,
in your experience, what is the lowest PSA you've seen with metastatic activity,
and so I think that there's a desire there to say, well if my PSA is over
a certain number maybe it's metastatic? So can you explain the ratios in that?
Yeah, the problem is is that there are many different types of prostate cancer, and some of
the prostate cancers make a lot of PSA; other prostate cancers make less PSA, and there are
types of prostate cancer that are actually angry or more aggressive variants that make relatively
little PSA. So, while generally speaking, higher PSA indicates more cancer cells and larger tumors,
that generality is only a generality and there are some very significant exceptions and PSA
should never be relied upon as the last word as to what's happening with your cancer.
Now we have all these new scans like PSMA PET scans that can tell you with far more precision
as to how much cancer is present, where is it located, and other scans, also, like MRIs and
color dopplers are useful for gauging what's going on with the cancer. [They are] much
more useful than PSA is. What you're asking is, can PSA be relatively low and
an individual still have a bad cancer that has spread somewhere around the body,
and the answer is yes, it can happen. It's not very common though. This is why PSA, in general,
is a good screening tool and in people that are diagnosed with PSAs less than 10 or 20 it's very
very rare for the cancer to be spread outside the prostate, but it can happen. There are variations
of prostate cancer that can metastasize even when the PSA is less than 10 or 20.
Taking cancer out of the equation, so let's just say in the cases of like prostatitis,
how high can the PSA get?
So, that's a great follow-up question because the converse, we were just talking about how
bad cancers can have low PSAs; I've seen men with PSAs of 30 or 40 that don't have any cancer with
carefully vetted evaluated people. We're sure that they don't have cancer;
they truly had PSAs of 30, 40, maybe even 50, and this is usually due to either
a massive prostate, severe prostatitis--I've seen prostatitis with PSAs as high as 80 or 90,
and or a combination of the two. This is a great example of how PSA is a really useful test,
but you always have to back it up with further evaluations to figure out what's really going on.
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