QUESTION: My father has been told he has prostate cancer. We have learned of treatment options but are unclear as to which is appropriate. What do you consider the best, surgery for removal? We are a black family. I say that because of my other question. Is prostate cancer more prevalent in blacks? If so, why? - Mrs. H.C.

ANSWER: Your last question first. Yes, it is surprising, but prostate cancer does have ethnic overtones. It is statistically more common in blacks than whites, and more so in whites than in Orientals, the lowest incidence group. Why this is so is a puzzle as yet unsolved.However, your father's cancer is the third most common kind among all men, right behind lung and colon cancer. The question of prostate cancer treatment always arises. The size of the cancer and the extent of spread are chief considerations in the options - whether outright gland removal, radiation or use of drugs to stem cancer growth (chiefly female hormones). Why female hormones? Because male hormones stimulate prostate cancer growth. Female hormones change the balance away from male hormones and help that way.

Mr. W.N. asks me if a prostate infection is a harbinger of prostate cancer to come. The answer is no. And while I am on this recurring subject, let me once again make a plea for early (40s at least) prostate examination. Early diagnosis means early and successful treatment. By age 40, no male physical examination is complete without this.

QUESTION: My great aunt, who is a spry 78 normally, has been quite sick lately with mononucleosis. Is it possible? I can't believe her doctor's diagnosis. I had it as a kid and other young friends had it. I never saw an adult with it and still haven't. - C.D.

ANSWER: The mono mail continues to come in. Mono is predominantly a young person's disease. No question about it. Its peak years are between 15 and 18. It is distinctly uncommon after age 40.

I am not joining you in your distrust of your aunt's doctor's diagnosis. It does occur rarely in elderly persons. But the symptoms differ a bit, fever being the prominent feature. The sore throat and enlarged nodes so common in childhood mono are usually less pronounced in the elderly, but fatigue does occur.

Much of my mail has to do with what has been called recurring mono - adult mono linked to the earlier childhood infection. This is a different matter, and there are, as I have noted, honest opinions that dispute this idea.

QUESTION: My husband has been diagnosed as having narcolepsy. Can he lead a normal life with treatment? - Mrs. J.J.

ANSWER: Certainly. Drugs help narcoleptics cope and lead quite normal lives. There isn't even a question about that today.

QUESTION: I'm a distance runner (45-50 miles a week). I sweat profusely even when I'm not running, but summer running has been a real hydration problem for me. Last year, I was put on lithium therapy for my manic-depressive condition. I am told that fluid and electrolyte levels are critical when on lithium. I want to keep up my running and my lithium treatment too. Any comment? - K.B.

ANSWER: You can do both. You must maintain your water and salt balance, however, for if you lose a lot of salt with your perspiration, your lithium blood level may rise to a higher concentration.

Make sure your fluid intake is generous and that you eat a normal diet that includes normal salt intake. You won't get into lithium trouble. If you haven't mentioned this to your doctor, do so. I am sure that he will insist on regular blood tests to measure lithium levels, if he is not already doing that. He'll be even more interested in having the tests if you explain your heavy perspiration problem.

FOR MRS. R. - The old idea that alcoholics face only liver damage as a consequence of abuse has been discarded. Today, we know that chronic alcohol abuse can cause serious heart muscle damage. That is called alcoholic cardiomyopathy. It can, of course, also damage the pancreas.

FOR MRS. G.G. - Will you have to watch out for diabetes now that your pregnancy-related sugar problem is passed? Yes, 40 percent of women who had gestational diabetes (diabetes during pregnancy) will develop outright diabetes within 10 years thereafter. So you must be alert to symptoms and be checked from time to time.

To learn the major categories of prostate troubles, their symptoms and treatments, read "Prostate Problems" (No. 26). Order by writing Dr. Donohue/No. 26, P.O. Box 830, Gibbstown, NJ 08027-9909, enclosing a long, stamped (52 cents), self-addressed envelope and $2.

Dr. Donohue welcomes reader mail but regrets that, due to the tremendous volume received daily, he is unable to answer individual letters. Readers' questions are incorporated in his column whenever possible.