Breast cancer rarely occurs in young women. Of the hundreds of thousands of breast cancers diagnosed worldwide, fewer than 0.1% occur in women under age 20 years; 1.9% between 20 and 34; and 10.6% between 35 and 44 (1,2).Although fewer than 7% of women diagnosed with breast cancer are younger than 40 years, more than 14,000 young women are diagnosed annually with invasive or noninvasive breast cancer in the United States alone, with thousands more diagnosed worldwide (3,4,5). Incidence rates appear to be stable over the past several decades in young women in the Western world, despite increases in mammography and reproductive and lifestyle trends (2,6) (Fig. 92.1) (3). A suggestion is that rates are increasing among young women, particularly in less-developed countries, but this may be owing to improvements in awareness, diagnosis, and reporting (7,8).

Despite the relative rarity of breast cancer in young women, it is the leading cause of cancer-related deaths in women under 40, and survival rates for young women with breast cancer are lower than for their older counterparts (4,9). The 5-year relative survival rate for women with breast cancer diagnosed before age 40 years is 82% compared with 89% for women diagnosed at age 40 or older (4). Although controversial, accumulating evidence suggests that young age is an independent risk factor for disease recurrence and death, despite that young women have conventionally received more intensive treatment than older ...