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Where does PSA come from?

DEAR DR. ROACH: Some 20 years ago, as I was turning 50, a biopsy confirmed prostate cancer. I elected to deal with that through surgery, a radical perineal prostatectomy. For the following 10 years, follow-up blood tests came back showing PSA at “less than 0.1,” which I interpreted to mean levels below the detectable limit. About 10 years ago the lab announced that they had improved their methods and would henceforth report PSA in blood as low as 0.01. Since then, my lab reports for PSA have been in the 0.02-0.04 range. Are there tissues that are not removed during a radical prostatectomy that could produce these low levels of PSA? Or are these some fugitive prostate cancer cells lurking somewhere? — D.A.S.

ANSWER: The term “prostate-specific antigen” isn’t exactly correct, because there are other cells in the body that produce PSA at very low levels. Urethral glands can, and so can salivary glands, normal breast tissue and some cancers besides prostate. The parallel structures to the prostate gland in women, Skene’s glands, may produce PSA, but not enough to register on a blood test.

When a PSA level that was previously undetectable after treatment such as surgery starts rising, it is almost always due to recurrence of cancer. However, this doesn’t seem to be the case for you. I suspect the very low levels you see now are either due to a very small amount of normal prostate tissue left after surgery or other tissues making PSA. Levels below 0.1 ng/mL are of uncertain significance, and the fact that they have stayed low for 10 or more years is good evidence that there has been no recurrence of cancer.

DEAR DR. ROACH: In 1976 I lost a lung to cancer. I have enjoyed my life and never had a problem. Recently, I fell on the golf course, and landed on my chest on the good lung side. When I hit the ground, I heard a loud crack. I had an X-ray that day, and was so happy the X-ray showed no broken bones. It did show two or three “calcium spots” in the remaining lung.

Over the years I have had numerous X-rays, and they have all been clear. My doctor didn’t seem concerned. I remember having pneumonia as a kid, but that was 75 years ago. Can you explain where these deposits come from? Should I be concerned? — S.C.A.

ANSWER: Calcium in the lung, most commonly a calcified pulmonary nodule, has a long list of possible causes. Previous infection is one. Tuberculosis and fungal infections very commonly leave behind calcified nodules that can be seen on X-ray. Benign tumors are other common causes of small areas of calcium. If the calcium spots are small (less than 5 mm), they are rarely anything to worry about. Many people may not even need a follow-up chest X-ray. However, in a person with a history of lung cancer, a follow-up chest X-ray or CT scan would be prudent. Your risk of developing another cancer almost 35 years later is small but not zero.

(Roach is a columnist for the North American Press Syndicate. Write to him at 628 Virginia Drive, Orlando, FL 32803.)

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