Author Topic: Cancer, Living With  (Read 13764 times)

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Offline Noisy Rhysling

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Re: Cancer, Living With
« Reply #150 on: October 05, 2019, 03:06:01 PM »
My doctor wants to do a PSA at my next routine blood work.  I tried to tell him that I'm probably not going to do anything regardless of the results, but he wasn't really listening.  I'm 42 years old, there's no history of prostate cancer in my family, and risks of false positive seem to me still to outweigh the likelihood of catching a curable, life-threatening prostate cancer. Sigh.
An elevated PSA means you should get checked. It's just a red flag. My PSA never went over 7 when I was Dx'd (via biopsy) back in '99.
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Online The Latinist

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Re: Cancer, Living With
« Reply #151 on: October 05, 2019, 03:32:35 PM »
An elevated PSA means you should get checked. It's just a red flag. My PSA never went over 7 when I was Dx'd (via biopsy) back in '99.

But the point is that I'm not going to have a biopsy if it comes back elevated anyway. The false positive rate of the test is so high and the likelihood that any cancer discovered is both treatable and needs to be treated now is so low, that the NNT of biopsy based on PSA alone doesn't justify it. All getting a screening will do is (potentially) create stress.
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Offline Noisy Rhysling

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Re: Cancer, Living With
« Reply #152 on: October 05, 2019, 05:30:09 PM »
An elevated PSA means you should get checked. It's just a red flag. My PSA never went over 7 when I was Dx'd (via biopsy) back in '99.

But the point is that I'm not going to have a biopsy if it comes back elevated anyway. The false positive rate of the test is so high and the likelihood that any cancer discovered is both treatable and needs to be treated now is so low, that the NNT of biopsy based on PSA alone doesn't justify it. All getting a screening will do is (potentially) create stress.
That's cool, if you don't have cancer.
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Online The Latinist

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Re: Cancer, Living With
« Reply #153 on: October 05, 2019, 05:41:56 PM »
An elevated PSA means you should get checked. It's just a red flag. My PSA never went over 7 when I was Dx'd (via biopsy) back in '99.

But the point is that I'm not going to have a biopsy if it comes back elevated anyway. The false positive rate of the test is so high and the likelihood that any cancer discovered is both treatable and needs to be treated now is so low, that the NNT of biopsy based on PSA alone doesn't justify it. All getting a screening will do is (potentially) create stress.
That's cool, if you don't have cancer.

I should not be having a PSA test. It's not medically justified because it is far more likely to cause unnecessary procedures and stress than it is to save my life. My doctor is insisting on ordering one; short of changing doctors (which I will consider), I can't get my A1C (which *is* medically justified) tested without it. So, believing that the downside outweighs the upside, what is the logical decision to make should the results of this unnecessary test come back positive?
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Offline Noisy Rhysling

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Re: Cancer, Living With
« Reply #154 on: October 05, 2019, 05:54:20 PM »
I wouldn't have any invasive procedure without a second opinion.
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Online bachfiend

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Re: Cancer, Living With
« Reply #155 on: October 05, 2019, 06:38:03 PM »
My doctor wants to do a PSA at my next routine blood work.  I tried to tell him that I'm probably not going to do anything regardless of the results, but he wasn't really listening.  I'm 42 years old, there's no history of prostate cancer in my family, and risks of false positive seem to me still to outweigh the likelihood of catching a curable, life-threatening prostate cancer. Sigh.
An elevated PSA means you should get checked. It's just a red flag. My PSA never went over 7 when I was Dx'd (via biopsy) back in '99.

My doctor insists on doing a PSA level annually, despite my thinking it’s a waste of time.  I’m 64, and my PSA level always comes in as below the normal range, so the only way it could change is to increase, possibly raising red flags.  Or I could have had a particularly hard session cycling.

I take consolation that if it ever happens that my doctor thinks a biopsy is necessary, which is a blind procedure, and can miss small tumours, I can insist on a nuclear magnetic scan first, to see if there’s a tumour present.  I think currently it wouldn’t be covered by medical benefits in Australia, and I’d have to pay the price myself (around $400), which I think is cheap, if it allows me to avoid an unnecessary biopsy.  And direct the biopsy if necessary.
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Offline lonely moa

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Re: Cancer, Living With
« Reply #156 on: October 06, 2019, 01:53:11 AM »
The GP insisted I have a PSA test last year.  He said it had been ten years since my last one.  I said I didn't really want one and he said if it comes back "one" we won't think about it again.  It cam back "one".  Job done. 

PSA tests are the male version of mammograms.  A black hole, really.
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Offline brilligtove

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Re: Cancer, Living With
« Reply #157 on: October 06, 2019, 06:21:59 AM »
Somewhere in my 40s m doctor asked me to do one as a baseline for future tests, rather than as a lone diagnostic test. That seemed like a reasonable thing to do.
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Online The Latinist

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Re: Cancer, Living With
« Reply #158 on: October 06, 2019, 08:22:41 AM »
Allow me to put some numbers to this:

The PSA test with a cutoff of 4 ng/mL has a sensitivity of just .205, meaning that 20.5% of people who have prostrate cancer will have a positive result.  Moreover, it has a specificity of .936, meaning that 93.6% of people who do not have prostate cancer receive a negative result. “But wait...” those of you who can subtract might be saying, “doesn’t that mean that 6.4% of people who take the test will receive a positive result even though they don’t have cancer?” Yep, it does.

But that doesn’t take into account prior probabilities at all. So what does that mean for me if I receive a positive result?

Well, as near as I can find, the prevalence of prostate cancer in those ages 40-44 is 0.000037, or .0037%. The likelihood that I have prostate cancer right now without any further testing are about .0037%. I think that everyone would agree that performing a biopsy based upon this knowledge alone would not be medically justified. That would mean everyone would be given an annual biopsy at huge risk and expense. But if we could add in a positive PSA result, what would be my likelihood of having cancer?  Surely it would go up?

Well, yes, of course it does.  But the question is by how much?  Applying a little Bayesian statistics to the question, we can figure this out.  I’ll spare you the math (though I’ll provide it if you want), but the upshot is that my likelihood of having cancer if I get a positive PSA is 0.000118506 or about 0.01%.  Yes, I’m three times as likely to have cancer as I was before the test, but the odds that I actually have cancer are still minuscule!  Moreover, the likelihood that My result is a false positive are 99.98%!

So, I ask you, do you think such a result really changes the calculus as to whether I should pursue further testing?

And this doesn’t even consider the likelihood that any cancer detected would actually ever become life-threatening (which is low). Nor does it take into account the risks of biopsy or the reduction in quality of life that could come with such treatment. Or the stress such a result would create even if I didn’t pursue further diagnostics.

Somewhere in my 40s m doctor asked me to do one as a baseline for future tests, rather than as a lone diagnostic test. That seemed like a reasonable thing to do.

I had not considered that, and I don’t know anything about the value of such a baseline. My doctor didn’t mention that.
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Offline brilligtove

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Re: Cancer, Living With
« Reply #159 on: October 06, 2019, 09:55:51 AM »
Allow me to put some numbers to this:

The PSA test with a cutoff of 4 ng/mL has a sensitivity of just .205, meaning that 20.5% of people who have prostrate cancer will have a positive result.  Moreover, it has a specificity of .936, meaning that 93.6% of people who do not have prostate cancer receive a negative result. “But wait...” those of you who can subtract might be saying, “doesn’t that mean that 6.4% of people who take the test will receive a positive result even though they don’t have cancer?” Yep, it does.

But that doesn’t take into account prior probabilities at all. So what does that mean for me if I receive a positive result?

Well, as near as I can find, the prevalence of prostate cancer in those ages 40-44 is 0.000037, or .0037%. The likelihood that I have prostate cancer right now without any further testing are about .0037%. I think that everyone would agree that performing a biopsy based upon this knowledge alone would not be medically justified. That would mean everyone would be given an annual biopsy at huge risk and expense. But if we could add in a positive PSA result, what would be my likelihood of having cancer?  Surely it would go up?

Well, yes, of course it does.  But the question is by how much?  Applying a little Bayesian statistics to the question, we can figure this out.  I’ll spare you the math (though I’ll provide it if you want), but the upshot is that my likelihood of having cancer if I get a positive PSA is 0.000118506 or about 0.01%.  Yes, I’m three times as likely to have cancer as I was before the test, but the odds that I actually have cancer are still minuscule!  Moreover, the likelihood that My result is a false positive are 99.98%!

So, I ask you, do you think such a result really changes the calculus as to whether I should pursue further testing?

And this doesn’t even consider the likelihood that any cancer detected would actually ever become life-threatening (which is low). Nor does it take into account the risks of biopsy or the reduction in quality of life that could come with such treatment. Or the stress such a result would create even if I didn’t pursue further diagnostics.

Somewhere in my 40s m doctor asked me to do one as a baseline for future tests, rather than as a lone diagnostic test. That seemed like a reasonable thing to do.

I had not considered that, and I don’t know anything about the value of such a baseline. My doctor didn’t mention that.

Thanks for the thorough breakdown. I understand how true/false positives/negatives work conceptually, but they tend to break my brain. I had a blood test alongside my regular blood tests, so there wasn't even an extra needle jab. I would likely have refused a biopsy based on the risk of infection and complications.

I don't have any stats on baseline testing, and didn't realize the true positive rate was that low. If the actual measurements is reasonably accurate a baseline could make sense.

I've now read your post three times. Well done!
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Online bachfiend

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Re: Cancer, Living With
« Reply #160 on: October 06, 2019, 05:19:26 PM »
PSA stands for prostate specific antigen.  It’s prostate specific, not cancer specific.

PSA testing should never have been allowed as a screening test.  It’s very useful when its level is very high.  If a person is known to have cancer, such as with secondaries elsewhere, and its level is very high, then it’s pretty certain the person has prostate cancer (women have an analogue of the prostate, and rarely they can have an equivalent of prostate cancer, in the same way that men can have breast cancer).

Or if the prostate cancer has been treated, such as removal of the prostate, and the PSA level - which initially after treatment was very low - and its level starts to increase, then it’s an indication that the cancer has recurred.

But if it’s used as a screening test, low increased or increasing levels of PSA don’t indicate cancer necessarily.  Another option other than blind biopsies, which are hit or miss (I used to be an anatomical pathologist.  The biopsies are very thin threads of tissue, usually 6 in number, and it wasn’t unusual for initial biopsies to be negative, and repeat biopsies to contain cancer in one of the threads), is to have a magnetic resonance scan of the prostate (if you have access to a facility, and can afford to pay for it), which will at least show whether you’ve got a tumour or not.  And a MRI is non-invasive.
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Offline Noisy Rhysling

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Re: Cancer, Living With
« Reply #161 on: October 06, 2019, 06:08:08 PM »
I don't think anyone goes from a positive test straight to the O.R.
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Online bachfiend

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Re: Cancer, Living With
« Reply #162 on: October 06, 2019, 07:08:54 PM »
I don't think anyone goes from a positive test straight to the O.R.

No, but they do go straight to a urologist.  A general practitioner getting a raised or increasing PSA level on a patient would be forced to refer a patient to avoid being sued for malpractice if the patient is shown later to have prostatic cancer that causes ‘harm.’  And urologists have an interest in operating.  It’s the way they make a living.

It’s been shown in many studies that if there’s a financial incentive in doing a procedure, then it tilts the decision making process towards doing the procedure rather than not doing it.

It’s simpler for a general practitioner not to do PSA testing as a screening procedure.  It’s justifiable, and the practice guidelines allow this.
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Offline Noisy Rhysling

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Re: Cancer, Living With
« Reply #163 on: October 06, 2019, 07:37:30 PM »
Weird.
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Online bachfiend

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Re: Cancer, Living With
« Reply #164 on: October 06, 2019, 07:48:28 PM »
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