Q: I am a 23-year-old female. I learned last April that I was dying of cancer. Two weeks after it was diagnosed, I left home.

I did not bother to go back to the doctor, because it was too painful to deal with the news of my condition.

Everyone in my family is still curious about my leaving my home and my job so abruptly. But I could not sit still knowing that I would be dying so early in life, when I had just begun to live.

To this day, I haven't told anyone in my family what is going on with me. I am really afraid to tell them because I don't want anybody to feel sorry for me.

Do you think that I should let my family know about my condition? I really feel guilty about not opening up to anyone, but I am so afraid.

A. Your reaction is classic, if extreme, and a familiar one to doctors, but it isn't wise. Even though you've probably always had a retiring, withdrawing nature, you've let it get way out of hand. You must see that you're being very unfair to your family and yourself.

A: You'd be appalled if your mother or father (or brother or sister) had been given this diagnosis and simply walked away without a word to you. You'd feel like they were turning away from your love -- and that's just what you're doing to them. These are the people who have nurtured you for 23 years and before. You can't deny their feelings, any more than you can deny your own. Tell them now. They have the right to stand by you and help you make sensible decisions.

Begin by checking the diagnosis thoroughly. The cure rate is particularly high at your age.

Your doctor may be one of the new breed who explains every possibility to his patients in full detail, which could have been so shocking that you only heard the worst possibility. advanced, too sophisticated to write off any cancer patient. According to Dr. Gregory Curt of the National Cancer Institute, 50 percent of all patients who are diagnosed with cancer this year will be cured, some with surgery, some with radiation, some with drugs, some with biological agents like interferon -- and many with a combined treatment.

No matter what your doctor told you, or what you think he told you, it isn't the last word. Before accepting any serious diagnosis -- or any surgery -- get a second and even a third opinion, and from an independent doctor. Look in The Directory of Medical Specialists in your public library for an oncologist connected with a regional cancer center or a university teaching hospital, where the best traditional and experimental work usually goes on.

He will need your records, which your first doctor will send him. They will help him compare the old test results with the new ones and also explain the original diagnosis to you.

You'll understand him better if you already know all about your particular kind of cancer and the various treatments for it. The more you know, the less frightened you'll be. For the best information, call the specialists at the Cancer Information Service (1-800-4-CANCER), which is part of the National Cancer Institute in Washington, D.C.

They will also send you an up-to-date list of the treatments under way all over the country (if you ask), which can help your doctor find a good program for you. To get into one at NIH, ask him to write the Clinical Center Review Board, Bldg. 10, Room 2-C-146 at NIH, Bethesda, Md. 20892 to see if you fit into one of their protocols. If you're accepted, they'll pay for any subsequent medical care, transportation and hotel care for out-patients.

The N.C.I. also has an excellent selection of free pamphlets and books. One of the best: "Taking Time," which deals with the emotional side of cancer. Write to the Office of Cancer Communications, N.C.I., Bethesda, Md. 20205 for a free copy. The American Cancer Society, with many offices around the country, is another good source of information.

You'll also want to take some family member to the doctor with you -- to ask the things that you forget -- and a recorder to tape the discussion. Most doctors don't mind because the tape can clarify confusions if it's replayed later.

Whatever the diagnosis, you'll want to deal with the consequences intelligently. Ask for a nurse-counselor to guide you or get in a support group, where you'll find some of the most remarkable people you'll ever meet: cancer patients who fight back. According to NIH, it's the fighters who live longest and are most likely to be cured.

You want to be one of them, but you can't win this battle alone. If you want to live, you have to try every trick you can find -- treatment, diet, counseling, prayer and the love of those who love you best.

You need your family and your family needs to be needed. The secret of confidence is the ability to confide in those you love.