IN-DEPTH REVIEW OF RESEARCH

Study background

With improved breast screening, breast cancer is detected at increasingly early stages. Diagnoses of ductal carcinoma in situ (DCIS), an early form of breast cancer, have risen as cases of later-stage breast cancer have fallen. Early detection of breast cancer is linked to better outcomes, less burdensome treatment and fewer related deaths. Most women with DCIS can be cured and have no subsequent breast cancer. However, 40 percent of women with DCIS have a second breast cancer, and 28 percent of those breast cancers are invasive.

The best treatment approach for DCIS is controversial. Concerns about overtreating DCIS for patients with low risk are weighed against concerns about undertreating those with higher risk. Better understanding the risk of individuals would inform and improve treatment decisions.

Beginning with 2000, the U.S. Census allowed people to identify as Native Hawai'ian and Pacific Islander (NHPI) separately from Asian Americans. Studies of NHPI people show that they generally have among the highest mortality rates from cancer, the highest rate of chronic disease and the shortest life span of groups in the U.S. Prior studies have shown that NHPI women have breast cancer four times more often than Asian American women. However, many studies continue to group NHPI with Asian American individuals, which limits our understanding of risk.

To better define the risk of a second breast cancer among women with DCIS, the researchers of this study evaluated cancer rates among different racial or ethnic groups in Hawai'i. Hawai'i is the most ethnically diverse U.S state, with the greatest percentage of NHPI women.

Researchers of this study wanted to know

Researchers wanted to know the risk of a second breast cancer among women from Hawai'i who had been diagnosed with ductal carcinoma in situ (DCIS).

Populations looked at in this study

This study included 6,221 women from the Hawai'ian Tumor Registry who were diagnosed with DCIS between 1973 and 2017. All women were age 20 or older and the majority (77%) were over 50 at the time of their diagnosis.

The patients included:

• 2,207 Japanese women (37%)
• 1,411 white women (23%)
• 840 Filipino women (14%)
• 821 Native Hawai'ian women (13%)
• 491 Chinese women (8%)
• Information about 388 other patients of other races or ethnicities (6%) were combined.

 Because the second diagnosis could have been a recurrence or residual cancer from their original DCIS, women were excluded if they had a second breast cancer diagnosis within six months of their DCIS diagnosis.

Study design

Information about women with DCIS was collected retrospectively from the Hawai'ian Tumor Register, one of the original National Institute of Cancer Surveillance, Epidemiology and End Result (SEER) registries. Researchers evaluated information about the original DCIS, including pathology, hormone receptor status and treatment received. They looked for statistical correlations between the original DCIS diagnosis, whether a woman had a second breast cancer, and if so, in which breast.

Study findings

Most women with DCIS did not have a second breast cancer.

Of the 6,221 women with DCIS:

• 5,777 (93%) had no second breast cancer within the time of the study.
• 441 (7%) were diagnosed with an invasive second breast cancer. Of these:
  • 190 had a second breast cancer in the same breast as the original DCIS.
  • 254 had a second breast cancer in the opposite breast.

Women under age 50 at the time of their original diagnosis were more likely to have a second breast cancer after DCIS than women over 50.

The frequency of second breast cancers differed among racial and ethnic groups.

After adjusting for age, cancer type, diagnosis year and time of first treatment, the frequency of second breast cancers in the same breast were evaluated in comparison to white women.

After adjusting for age, cancer type, diagnosis year and time of first treatment, the frequency of second breast cancers in the opposite breast were evaluated in comparison to white women.

The rate of a second breast cancer after DCIS differed depending on the treatment received for the original DCIS.

Researchers looked at how often women had second breast cancers in the same breast compared to women who had breast-conserving surgery (BCS) only.

*Systemic therapy includes chemotherapy and/or hormonal therapy

Researchers also reviewed how often women had second breast cancers in the opposite breast compared to women who had breast-conserving surgery (BCS) only.

*Systemic therapy includes chemotherapy and/or hormonal therapy

One caveat is that underlying differences based on pathology or receptor status in each group of women may make them more or less likely to have a second breast cancer (e.g., some other factor may have put women who received systemic therapy after mastectomy at higher risk).

Strengths and limitations

Strengths

• This study looked at a large group of racially and ethnically diverse women, including those of Native Hawai'ian, Filipino, Chinese and Japanese ancestry. Unlike studies in which white women were the overwhelming majority and other groups are statistically underrepresented, this study allows a more accurate determination of risk for several groups.
• Differences in treatment approaches were evaluated and linked to different rates of second breast cancers.

Limitations

• This is a retrospective anonymous analysis, so some information was incomplete. The hormone-receptor status was missing for 40 percent of patients, preventing conclusions about its impact on second breast cancers.
• This study used data from the Hawai'ian Tumor Registry and may not reflect rates of second breast cancers in other geographical regions of the U.S. or among other racial groups (e.g., African American or Hispanic American women).

Context

Prior studies have shown variations in the risk of second breast cancer among people of different ethnicities or races. African American women have higher rates of a second breast cancer in the same or opposite breast than white women. Hispanic women have a higher rates of secondary breast cancer in the same breast as compared to white women. Some studies show that Asian American and Pacific Islander women have similar rates of second breast cancers compared to white women. However, experts now recognize that grouping Native Hawai'ian and Pacific Islander women with Asian American women may mask underlying differences.

Conclusions

This study indicates that race and ethnicity are important factors in understanding the risk of second breast cancer among women with DCIS. Hawai'ian, Filipino and Japanese women may have a higher risk of secondary breast cancer than previously recognized. Women with DCIS under age 50 may also be at greater risk than those diagnosed at older ages. Improving our understanding of the risk of subsequent breast cancer may allow for treatment decisions that better fit patients. This study and others highlight the importance of assessing the risk for racial and ethnic groups independently so that the decreased risk of one group does not mask the increased risk of another group.

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posted 3/15/22