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Some Thoughts on Numbers

By Heather Millar

Numbers

At my oncology check-up earlier this month, I ran into an elegant woman in the waiting room of the Breast Care Center. I commented on how put together she is, what a contrast with my own sweaty self!

The elegant woman and I started talking. She was newly diagnosed. I should have realized that she had that “deer in the headlights” look about her. Her equally elegant husband looked similarly dazed. They held hands as if they were holding on for dear life.

The two of them brought me right back to those early days after diagnosis. It’s amazing that any of us survive it: that firestorm of emotions that we attempt to put out with a fire hose of information. How to become a cancer “expert” in three days flat! How to deal with the varied, and sometimes crazy, reactions of friends and family! How to deal with our own, sometimes crazy, reactions and fears!

The elegant woman was not going to see my oncologist, but another doctor whom I know to be well respected. I told her the doctor has a great reputation and that I didn’t think she could come to a better place for advice. She said that she and her husband live in Folsom, just outside of Sacramento, in the foothills of the Sierra Nevada mountains, and she’s coming to UC-San Francisco for a second opinion.

I nodded. I wondered why she hasn’t gone to UC-Davis, a medical center much closer to her home. I wondered why she’s picked one oncologist and not another. I wondered if I would be comfortable doing my treatment at a smaller, local hospital. I said none of these things. It doesn’t take long in cancer support groups or clinics to realize that you can share your experience, but you can’t make decisions for anyone else. Each patient must walk their own road, in their own way.

I thought about how many decisions face the elegant woman right now: Lumpectomy or Mastectomy? If mastectomy, will she do reconstruction? Chemo or no chemo? What kind of chemo? Genetic testing or not? Oncotype testing (a profile of the cancer’s genes) or not? Radiation or not? Hormone treatment or not? Continue working, or not?

In addition to the fear and confusion, she must now make a million decisions. Almost all of these decisions come down to numbers. How will one treatment reduce risk? What percentage of patients have problems with this or that treatment? How will her survival be enhanced with a particular medicine or surgery?

Don’t stop reading! I promise this won’t be a math class. But mastering a little math is important to your survival. I feel your pain: While I have been interested in science, health, and technology for most of my career, my last math class was high school calculus. Numbers have always been more difficult for me than words. But I think all cancer patients need to get a handle on a few number concepts.

Check out the famous essay by Stephen Jay Gould, the witty Harvard biologist who beat mesothelioma for 20 years before dying in 2002. Gould’s meditation on statistics, “The Median is Not the Message,” should be required reading for all cancer patients.

The take-away from Gould’s essay is the first math concept that every cancer patient should master:

• The “median survival” number is not fate. It is simply a middle point. Let’s say a doctor tells you that the “median survival” for your type of cancer is one year. That means half of the patients lived less than 1 year. But half lived longer. Shoot to be part of the latter group.

A couple other math points that I’ve found useful:

• There’s a difference between risk increase or decrease and “absolute” risk increase or decrease.

Let’s say a type of chemotherapy increases a risk of a particular side effect by 50 percent. That’s not necessarily as bad as it sounds. If the “absolute risk” of the side effect is 1 percent , then a 50 percent increase with the chemo only brings the “absolute increase” from 1 percent up to  1.5 percent. That may be perfectly acceptable.

It can also go the other way: things may not be as good as they sound. Generally, docs will tell you that getting radiation after chemo and surgery will decrease your chance of a breast cancer recurrence by 15 percent. So let’s say that 15 percent of breast cancer patients have a risk of recurrence in the first five years. That’s the “absolute risk,” 15 chances out of 100.

Getting radiation doesn’t bring that risk to zero: 15 minus 15. Rather, it cuts that “absolute risk” by 15 percent. In other words, it’s not a subtraction problem but a percentage problem. What’s 15 percent of 15? My calculator says it’s 2.25.

So radiation knocks the “absolute risk” down 2.25 percentage points, from a 15 percent risk to a 12.75 percent risk, 12.75 chances out of 100. That’s not nothing, but neither is it a “get out jail free” card.

• When you’re looking at the pros and cons of a certain type of screening or treatment, watch out for a problem called “lead time bias.”

Let’s say there are two twin sisters. One gets a mammogram at 40, gets diagnosed with cancer, gets treatment and lives until 65.  Her survival is 25 years.

The other sister doesn’t get a mammogram until 50. She also gets diagnosed, has treatment and lives until 65, but her survival is only counted to be 15 years, since her diagnosis came later.

The sisters may have the same type of slow-growing cancer, but because one was diagnosed earlier, it seems that her treatment helped her live longer. This doesn’t mean that treatment didn’t work as well for the sister diagnosed later, only that the survival numbers aren’t as absolute as they appear to be.

If you’re still with me, then you’re probably thinking, “Man, math is scary.” So is cancer, right?

You don’t have to get an MD or a Ph.D. But really understanding the numbers will help you navigate through Cancerland. If you’re feeling overwhelmed by the statistics your doctor is citing, don’t be afraid to ask for clarification. Ask, then ask again if you need to do so. Understanding the numbers, you can make your own decisions with confidence, as I hope the elegant lady will.

Photo: iStockphoto

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