Given the relative odds, one would think Gessen’s genetic counselors would have advised a pre-emptive mastectomy rather than an oophorectomy, or removal of the ovaries. To her surprise, they recommended an oophorectomy. One can understand their logic: breast cancer is easier to detect and survive; removing the ovaries reduces the risk of breast cancer; and most women can’t even countenance the idea of parting with their breasts. But Gessen balked, well aware of the studies associating surgical menopause with cognitive troubles and depression, to say nothing of osteoporosis, high blood pressure and heart disease. “I politely suggested I could just shoot myself tomorrow: That would prevent my death from cancer with a 100 percent probability,” she writes. “The joke remained suspended in the thin air between us and the counselors, and with it, our disengagement from one another was complete.”

Image Credit... Ellen Lupton

So Gessen ditches the counselors and the doctors and instead tries to collect information from a wider, more eccentric variety of sources. A sympathetic nurse scientist at the Dana-Farber Cancer Institute concedes that close surveillance might be a reasonable alternative to surgery for some women. Nancy Etcoff, a psychologist at Harvard Medical School and the author of “Survival of the Prettiest,” a study of the evolutionary importance of beauty, points out that while breasts are central to female attractiveness, attractiveness and happiness are barely correlated. Most memorably, an instructor in a psychology and economics class at Harvard attempts to “express life in numbers” for Gessen on an Excel spreadsheet, assigning values to living with cancer, living without cancer and living with the stench of a cancer threat. Though she rejects some of his findings  I will not say what Gessen ultimately chooses to do  she leaves his office feeling light, unburdened: “I jumped on my bicycle and sped home, making currents in the puddles, getting soaked, feeling strong and a little silly and generally like my life had a utility of 100 a year, possibly even more, now that I also felt that much more competent for being able to put a number on the value of riding in the rain.”

Our culture doesn’t yet have the infrastructure  educational, medical, moral, the whole shebang  to handle the consequences of the recent revolution in genetic testing. But we’ll need it, and Gessen, though drafted into this project against her will, is helping to do the crucial spadework to build it. As she points out, the nascent rules of the new cancer caste to which she belongs “are an approximation, albeit a very crude one, of the rules by which my daughter’s generation will run its life.”

And indeed, “Blood Matters” is about far more than Gessen’s own story. She writes energetically, if a bit discursively at times, about the grander context in which her personal drama takes place. There’s a lovely chapter about Holmes Morton, who, long before the term “personalized medicine” entered our lexicon, was developing protocols to treat genetic diseases common to the Amish and the Mennonites. Henry T. Lynch, the doctor who first posited that cancer might have a genetic component (and one of the first to talk about preventive surgery), earns a chapter, as does a group of people living with the mutation for Huntington’s. Gessen ponders behavior and genetics (characterizing herself as a “novelty-seeking, sex-crazed, egomaniacal optimist”  until she discovers she has a mutation associated with harm-avoidance and anxiety), and she writes thoughtfully about Dor Yeshorim, a premarital testing program aimed at Orthodox Jews, which avoids telling individuals whether they carry a gene for one of the “Jewish mutations” by telling them instead if they’re genetically compatible with the person they wish to marry. (“Why advise people if they don’t need to know?” asks a rabbi who once ran the program.)

My only quarrels with “Blood Matters” come at the beginning and at the end. Gessen starts with a lengthy disquisition about Jews, disease and selective advantage, leading us to believe we’re in for a treatise on Jewish exceptionalism, when in fact the questions she addresses are universal. And for a book that’s so careful, she concludes uncarefully, asking and too easily answering all sorts of questions about the moral consequences of genetic advancements that deserve more nuance. (She tries to make the case, for instance, that prospective parents already preselect embryos for intelligence, because it’s common in the United States to terminate pregnancies involving sex-chromosome abnormalities that correlate with learning problems and below-average intelligence  as if the fear of sex-chromosome abnormalities themselves, not the desire for smarter children, isn’t still the reason.)