单选题 Breast cancer is second only to skin cancer as the most common malignancy diagnosed in women in the United States. In 2001, about 192, 200 new cases of invasive breast cancer were diagnosed and 40, 200 women died of the disease. Only lung cancer accounts for more cancer deaths in women. The incidence of breast cancer has increased over the last 20 years. Although some of the increase can be attributed to changes in reproductive patterns, such as delayed childbearing and having fewer children, much of the rise is due to the increased detection of smaller, earlier-stage cancers with the widespread adoption of mammography screening in asymptomatic women. According to data from the Surveillance, Epidemiology, and End Results Program, incidence rates of tumors less than 2. 0 cm in diameter more than doubled from 1980 to 1987, whereas rates of tumors greater than 3. 0 cm decreased by 27%. In particular, incidence rates of in situ breast cancer have risen dramatically over the last 25 years. The annual increase in age-adjusted ductal carcinoma in situ incidence rates from 1983 to 1992 was 17. 5%. Although the incidence of breast cancer has been increasing, there has been a decline in breast cancer mortality. Death rates decreased 1. 6% annually between 1989 and 1995, then 3. 4% annually between 1995 and 1998. This improvement in the mortality rate has been attributed to both mammography screening and improvements in breast cancer treatment. Breast cancer has a number of identifiable risk factors. Aside from a personal history of breast cancer, the most important risk factor in women is age. Between 1994 and 1998, 77% of new cases of breast cancer and 84% of breast cancer deaths occurred in women older than 50 years. Other nonmodifiable risk factors include family history, age at birth of the woman's first child, early menarche, and late menopause. Potentially modifiable risk factors include alcohol consumption, use of postmenopausal hormones, and obesity after menopause. Risk factors and their relative risk are listed in table 1 in order of the strength of their association. Although most breast cancer cases are sporadic, up to 10% are linked to genetic predisposition. Women with a family history of breast cancer, especially in a first-degree relative (ie, mother, sister, or daughter), have an increased risk of breast cancer. In general, a "positive family history" of breast cancer confers a relative risk of 2. 0 to 3. 0, with the degree of risk varying directly with the closeness of the relationship. Paternal and maternal relatives with breast cancer contribute similarly to the increased risk. Most women with a family history of breast cancer do not have a history striking enough to suggest the presence of an inherited breast cancer syndrome. In many cases, primary care physicians can readily distinguish between families with heritable cancers and those with several sporadic cases. Women at high risk of inherited breast cancers typically have several relatives with breast cancer diagnosed before age 45 to 50 and may also have a family history of bilateral breast cancer, ovarian cancer, or male breast cancer.

【正确答案】 A

【答案解析】解析：推理题。根据第二段Although some of the increase can be attributed to changes in reproductive patterns，…，much of the rise is due to the increased detection of smaller, earlier-stage cancers with the widespread adoption of mammography screening in asymptomatic women．(尽管乳腺癌发病率的提高一部分可以归咎于繁殖方式的变化，……，但是主要还是因为随着乳腺扫描仪的发明许多无症状病例和早期病例被发现造成的。)可以推断出过去乳腺癌发病率较低的原因之一可能是由于没有发明出乳腺扫描仪，故许多无症状病例未被发现。