Breast Cancer Facts & Figures 2019-2020 (part 2)
Breast Cancer Facts & Figures 2019-2020
What is breast cancer?
Breast cancer is a group of diseases in which cells in breast tissue change and divide uncontrolled, typically resulting in a lump or mass. Most breast cancers begin in the lobules (milk glands) or in the ducts that connect the lobules to the nipple.
What are the signs and symptoms of breast cancer?
Breast cancer typically has no symptoms when the tumor is small and most easily treated, which is why screening is important for early detection. The most common physical sign is a painless lump. Sometimes breast cancer spreads to underarm lymph nodes and causes a lump or swelling, even before the original breast tumor is large enough to be felt. Less common signs and symptoms include breast pain or heaviness; persistent changes, such as swelling, thickening, or redness of the skin; and nipple changes, such as spontaneous discharge (especially if bloody), scaliness, or retraction. Any persistent change in the breast should be evaluated by a physician.
How is breast cancer diagnosed?
Breast cancer is typically detected either during screening, before symptoms have developed, or after a woman notices a lump. Most masses seen on a mammogram and most breast lumps turn out to be benign (not cancerous). When cancer is suspected, tissue for microscopic analysis is usually obtained from a needle biopsy (fine-needle or larger core-needle) and less often from a surgical biopsy. Selection of the type of biopsy is based on multiple factors, including the size and location of the mass, as well as patient factors and preferences and resources.
How is breast cancer staged? The extent of the cancer and its spread at the time of diagnosis determines its stage, which is essential for guiding treatment options and prognosis (prediction of disease outcome). The two main staging systems for cancer are the American Joint Committee on Cancer (AJCC) staging system, typically used in clinical settings, and the Surveillance, Epidemiology, and End Results (SEER) summary staging system, used for descriptive and statistical analysis of tumor registry data. The AJCC system was recently updated (effective January 2018) to add prognostic stage groups.1 AJCC anatomic stage is based on extent of the cancer (in the breast, regional lymph nodes, and distant spread), while prognostic stage also includes information on the presence of estrogen receptors (ER), progesterone receptors (PR), levels of human epidermal growth factor receptor 2 (HER2, a growth-promoting protein) and/or extra copies of the HER2 gene (HER2+/HER2-), and grade (reflecting how closely the cancer’s microscopic appearance looks like normal breast tissue). In this document, we generally refer to the SEER summary stage except in the section on the description of breast cancer treatment (page 23), which references AJCC anatomic stage. According to the SEER summary stage system: • In situ stage refers to the presence of abnormal cells that are confined to the layer of cells where they originated. • Local stage refers to invasive cancer that is confined to the breast. • Regional stage refers to cancer that has spread to surrounding tissue and/or nearby lymph nodes. • Distant stage refers to cancer that has spread to distant organs and/or lymph nodes, including nodes above the collarbone.
What are the types of breast cancer?
In Situ
Historically, ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS), also known as lobular neoplasia, were considered the two main types of in situ breast cancer. However, LCIS is generally believed to be a benign condition associated with increased breast cancer risk, but without the potential to progress to invasive cancer, so it was removed from the latest edition of the AJCC breast cancer staging system.2 DCIS, on the other hand, is a precursor to invasive cancer, although not all DCIS progresses. In fact, DCIS sometimes grows so slowly that even without treatment it would not affect a woman’s health. Long-term studies have found that only 20%-53% of women with untreated DCIS are ultimately diagnosed with invasive breast cancer.3-5 DCIS patients who are premenopausal at diagnosis or who had their DCIS detected by palpation are at greater risk of being diagnosed with a future invasive breast cancer.6, 7 During 2012-2016, DCIS represented 16% of all breast cancer diagnoses.8
See page 13 for additional information on DCIS and LCIS. More information can also be found in the Cancer Facts & Figures 2015, Special Section: Breast Carcinoma In Situ.
Invasive
Most (81%) breast cancers are invasive, or infiltrating, which means the abnormal cells have broken through the walls of the glands or ducts where they originated and grown into surrounding breast tissue. Although breast cancer was historically referred to as a single disease, it is now considered a group of diseases, consisting of four major molecular subtypes and at least 21 distinct histological subtypes (type of tissue in which the cancer originates) that differ in risk factors, presentation, response to treatment, and outcomes.
Histologic subtypes
Histology is based on the size, shape, and arrangement of breast cancer cells. More than 75% of invasive breast cancers are now histologically categorized as “no special type,” historically called “ductal” carcinomas.8 The most common special histologic subtype is invasive lobular
carcinoma, representing about 15% of invasive breast cancers.8 Tubular, mucinous, cribriform, and papillary carcinoma are rare breast cancer subtypes that are generally associated with favorable prognoses.9 Inflammatory breast cancer is an uncommon but aggressive type of breast cancer that is characterized by swelling and redness of the skin of the breast. Molecular subtypes Breast cancer molecular subtypes are determined through gene expression analysis, a costly and complicated process that is not currently standard clinical practice. However, these subtypes can be approximated using routine methods for clinical evaluation of biological markers (ER, PR, HER2, and sometimes others). Hormone receptor positive (HR+) cancers are those that test positive for ER or PR, or both. Information about grade and proliferation (rate of cell division) is also sometimes used to assign subtype. The four main molecular subtypes are described below. It is worth noting that there are overlaps between categories and the clinical approximations do not perfectly correspond to the molecular breast cancer subtypes as described on the next page.10
Luminal A (HR+/HER2-): This is the most common type of breast cancer (Figure 1) and tends to be slower-growing and less aggressive than other subtypes. Luminal A tumors are associated with the most favorable prognosis in part because they are usually responsive to hormonal therapy (see page 26).11, 12
Luminal B (HR+/HER2+): In addition to being HR+, this subtype was originally characterized clinically as always being positive for HER2, but more recently has been defined by being highly positive for the protein Ki67 (an indicator of a large number of actively dividing cells) and/or HER2. Luminal B breast cancers tend to be higher grade than luminal A and thus are associated with poorer outcomes.11, 12
Basal-like (HR-/HER2-): These cancers are also called triple negative because they are ER-, PR- and HER2-. Themajority (about 75%) of triple negative breast cancers fall in to the basal-like subtype defined by gene expression profiling.13 Triple negative breast cancers have a poorer prognosis than other subtypes, in part because treatment advances have lagged behind other molecular subtypes. 14, 15 These cancers occur at twice the rate in black women compared to white women in the US, and are also more common in premenopausal women and those with a BRCA1 gene mutation.16
HER2-enriched (HR-/HER2+): In the past, this subtype had the worst prognosis; however, the widespread use of targeted therapies for HER2+ cancers has substantially improved outcomes for these patients.14, 17 For more information about the treatment of HER2+ breast cancers, see the section on targeted therapy on page 26
Breast Cancer Occurrence
How many cases and deaths are expected to occur in 2019? In 2019, an estimated 268,600 new cases of invasive breast cancer will be diagnosed among women (Table 1) and approximately 2,670 cases will be diagnosed in men. In addition, an estimated 48,100 cases of DCIS will be diagnosed among women. Approximately 41,760 women and 500 men are expected to die from breast cancer in 2019.
How many women alive today have ever had breast cancer?
More than 3.8 million US women with a history of breast cancer were alive on January 1, 2019.18 Some of these women were cancer-free, while others still had evidence of cancer and may have been undergoing treatment. More than 150,000 breast cancer survivors are living with metastatic disease, three-fourths of whom were originally diagnosed with stage I-III.19
What is the risk of being diagnosed with breast cancer?
Approximately 1 in 8 women (13%) will be diagnosed with invasive breast cancer in their lifetime and 1 in 39 women (3%) will die from breast cancer (Table 2).20 Lifetime risk is an average of risk for all women and accounts for deaths from other causes that may preempt a breast cancer diagnosis. Breast cancer risk varies by age and race/ethnicity:
Age
• Breast cancer incidence and death rates increase with age until the seventh decade (Figure 2). The decrease in incidence rates that occurs in women 80 years of age and older may reflect lower rates of screening, the detection of cancers by mammography before 80 years of age, and/or incomplete detection.
• During 2012-2016, the median age at the time of breast cancer diagnosis was 62.20 This means that half of women who developed breast cancer were 62 years of age or younger at the time of diagnosis. The median age of diagnosis was slightly younger for black women (60) than white women (63).20
• Table 2 provides 10-year probabilities of invasive breast cancer diagnosis or death for women of different ages. By 10-year age groups, the probability of a breast cancer diagnosis is highest for women in their 70s (4.1%), while breast cancer death is most likely among women in their 80s (1.0%)
Race/Ethnicity
• Breast cancer incidence and death rates by race and ethnicity during the most recent time period are shown in Figure 3. Incidence rates are highest among non-Hispanic (NH) whites (130.8 per 100,000), followed closely by NH blacks (126.7). However, NH black women have the highest breast cancer death rate (28.4 deaths per 100,000), more than double that in Asian/Pacific Islander (API) women (11.5), who have the lowest incidence and death rates.
• The distributions of breast cancer subtypes for the major racial/ethnic groups are shown in Figure 4. HR+/HER2- breast cancers are by far the most common subtype among women of all races/ ethnicities. About 21% of breast cancers in NH black women are triple negative, which is about double the proportion of this subtype in other racial/ethnic groups. The higher breast cancer death rate in black women in part reflects the disproportionate burden of triple negative breast cancers in this group.
Stage
• At the time of diagnosis, approximately 64% of breast cancer patients have local-stage breast cancer, 27% have regional stage, and 6% have distant (metastatic) disease.
• Stage at diagnosis also varies by race/ethnicity (Figure 5). NH black, Hispanic, and American Indian/Alaska Native (AIAN) patients are less likely to be diagnosed with local-stage disease (56%-60%) compared to NH white and API patients (64%-66%).
How has the occurrence of breast cancer changed over time?
Incidence Incidence rates of DCIS and invasive breast cancer rose rapidly during the 1980s and 1990s (Figure 6), particularly among women 50 years of age and older, largely due to increases in the prevalence of mammography screening, which increased from 29% in 1987 to 70% in 2000.21 For example, DCIS rates among women 50 and older, increased more than 11-fold from 1980 (7 cases per 100,000) to 2008 (83 cases per 100,000).
In contrast, there was a sharp drop (nearly 13%) in the invasive breast cancer rate between 1999 and 2004, believed to be largely due to the decreased use of menopausal hormones following the 2002 publication of clinical trial results that found higher risk of breast cancer and heart disease among menopausal hormone users, and may also reflect small declines in mammography screening since 2000.22, 23 The decline in breast cancer incidence occurred primarily in white women, in those 50 years of age and older, and for ER+ disease.22, 24
In the most recent time period (2012-2016), the DCIS rate declined by 2.1% per year8 and the invasive breast cancer incidence rate rose by about 0.3% per year.20 In fact, the incidence rate for invasive breast cancer has been slowly increasing since 2004.20 A recent study concluded that increases in body mass index (BMI) and declines in the average number of births per woman (both breast cancer risk factors) have likely contributed to the recent increase in incidence.25
Race/Ethnicity
Figure 7 presents trends in invasive female breast cancer incidence rates by race and ethnicity since 2001 based on data from 45 states, representing 92% of the US population. During the most recent 5 years of available data (2012 to 2016), overall breast cancer incidence rates increased most rapidly among APIs (1.5% per year), followed by AIANs (0.8% per year), and NH blacks and NH whites (both 0.5% per year), but were relatively stable in Hispanics.
Stage
The overall increase in breast cancer incidence is largely because of an increase in local-stage disease. From 2012 to 2016, the incidence rate increased by 1.1% per year for local-stage breast cancer, but declined by 0.8% per year for regional-stage disease, which may reflect a shift toward earlier stage at diagnosis. The incidence rate for distant-stage disease increased 2.5% annually during 2001-2011, but has since stabilized. The increase in distant-stage disease may be partly explained by the decrease in unknown stage, because of more complete staging of advanced tumors.26 This trend may also reflect increased detection of asymptomatic metastases due to the rise in the use of advanced imaging.
Mortality
The overall breast cancer death rate increased by 0.4% per year from 1975 to 1989, but since has decreased rapidly, for a total decline of 40% through 2017. As a result, 375,900 breast cancer deaths were averted in US women from 1989 to 2017. However, the decline in breast cancer mortality has slowed slightly in the most recent time period, from an annual decrease of 1.9% during 1988-2011 to 1.3% during 2011-2017. By race/ethnicity, the breast cancer death rate during 2013-2017 declined annually by 2.1% in Hispanics, 1.5% in NH blacks, 1.0% in NH whites, and 0.8% in APIs, but was stable in AIANs (Figure 8)
The decline in breast cancer mortality has been attributed to both improvements in treatment and earlier detection.27 However, not all women have benefited equally from these advances, as indicated by the striking divergence in mortality trends between black and white women beginning in the early 1980s (Figure 8). This disparity likely reflects a combination of factors that are difficult to parse, including later stage at diagnosis and other unfavorable tumor characteristics, higher prevelance of obesity and other health conditions, less access to high-quality prevention, early detection, and treatment.28, 29 For example, black women are more likely to be screened at lower resourced and nonaccredited facilities and also experience longer intervals between mammograms, and between abnormal results and follow-up.30-33 Although self-reported screening rates based on national surveys are similar between black and white women, studies indicate that black (and Hispanic) women are more likely than white women to overestimate their screening history.34-36 The black-white disparity has grown as treatment for breast cancers has improved (particularly for HR+ breast cancers), but appears to have peaked in 2011, when rates in NH black.
women were 44% higher than those in whites. In the most recent period (2013-2017), the breast cancer death rate was 40% higher in black women versus white women (Figure 3)
Are there geographic differences in breast cancer patterns?
Table 3 shows variation in state-level breast cancer incidence and death rates per 100,000 women by race/ ethnicity. Although the overall incidence rate for breast cancer in the US remains slightly higher in NH white women compared to NH black women, rates are higher in NH black women in 4 of the 43 states with reliable data for both groups (Louisiana, Mississippi, Oklahoma, and Wisconsin), and are not statistically different in 26 other states and the District of Columbia.37 Data for AIAN women are too sparse to provide by state; however, during 2012-2016, incidence rates were more than twofold higher among women in Alaska (139.7 per 100,000) and the Southern Plains (150.8 per 100,000) compared to those living in the Southwest US (60.4 per 100,000).8
In contrast to incidence, breast cancer death rates are higher among NH black women than NH white women in every state, with rates in some states (e.g., Louisiana and Mississippi) as much as 60% higher (Table 3). Death rates reflect both cancer incidence and survival. Breast cancer mortality rates among NH white women tend to be highest in the North Central, Mid-Atlantic, and Western regions of the US (Figure 9). Among NH black women, the highest death rates are found in some of the South Central and Mid-Atlantic states, as well as California. Factors that contribute to geographic disparities include variations in risk factors and access to screening and treatment, which are influenced by socioeconomic factors, legislative policies, and proximity to medical services.
During 2013-2017, breast cancer death rates decreased in all states except Nebraska.37 In addition, the decline in breast cancer mortality has leveled off for black women in Colorado and Wisconsin and for white women in Nebraska, Texas, and Virginia. Notably, during 2016-2017, breast cancer was the leading cause of cancer deaths (surpassing lung cancer) in 6 states (Arizona, Colorado, Florida, Georgia, Mississippi, and South Carolina) among black women and in Utah among white women.37
Breast cancer survival
Race/ethnicity
Male breast cancer
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