DCIS in HK: Increased mortality rate despite excellent long-term survival

Despite excellent long-term survival, patients with ductal carcinoma in situ (DCIS) in Hong Kong have higher mortality rate compared with the general population of women, according to results of a 10-year retrospective cohort study based on territory-wide data from the Hong Kong Cancer Registry.

“Population-wide breast cancer screening is not currently implemented in Hong Kong. We believe our study’s findings support further investigation of the cost-effectiveness of implementing a population-wide breast cancer screening programme,” said the researchers. [Hong Kong Med J 2020;26:486-491]

In the study, data of all patients (n=1,391) diagnosed with DCIS in Hong Kong in 1997–2006 were extracted from the Hong Kong Cancer Registry, a population-based cancer registry for all patients diagnosed with cancer in public and private medical institutions in Hong Kong since 1963.

Overall, the incidence of DCIS almost doubled from 1997–2001 (n=449) to 2002–2006 (n=889). The mean age of DCIS diagnosis was 49.2 years. More than half (51.2 percent) of the DCIS patients underwent mastectomy, while 28.7 percent underwent breast-conserving surgery. Nearly a third (29.5 percent) of patients had adjuvant radiotherapy and 15.9 percent received hormonal therapy with tamoxifen.

At a median follow-up of 11.6 years, the 5-year and 10-year breast cancer–specific mortality rates were 0.3 percent and 0.9 percent, respectively. Invasive breast cancer eventually developed in 7.8 percent of the cohort, with the incidence of breast cancer being comparable between 1997–2001 and 2002–2006 (8.2 percent vs 7.6 percent).

HER2-positive DCIS was associated with a significantly increased 10-year breast cancer–specific mortality rate  compared with HER2-negative DCIS (2.9 percent vs 0 percent; p=0.0181). On the other hand, patients with oestrogen receptor (ER)–positive DCIS had a numerically lower 10-year breast cancer–specific mortality rate than those with ER-negative DCIS (0.8 percent vs 1.0 percent). The histology grading of DCIS had no effect on 10-year breast cancer–specific mortality rate (low-/intermediate-grade DCIS vs high-grade DCIS, 0.5 percent vs 0.8 percent; p=0.6776).

The breast cancer–specific mortality rate was 2.2 per 100,000 population in patients aged 30–34 years and 34.8 per 100,000 population in those aged 60–64 years, with a standardized mortality ratio (SMR) of 5.7 (95 percent confidence interval, 3.7 to 8.3) for patients with DCIS compared with the general population.

“The doubling of DCIS incidence between 1997–2001 and 2002–2006 might be explained by improved patient education at individual and population levels in terms of breast cancer awareness, resulting in increased rates of self-initiated breast cancer screening over the past decade,” the researchers suggested.

“The mortality rate of patients with DCIS in Hong Kong has remained stable over the past few decades, despite improved detection of breast cancer during the same period. The 10-year breast cancer–specific mortality rate is comparable with findings in the West,” they noted, suggesting that factors leading to improved survival of patients with DCIS is likely multifactorial, and may be due to earlier detection and improved surgical oncologic treatment as well as overdiagnosis of DCIS.”

“Our finding of an association between HER2-positive DCIS and increased 10-year breast cancer–specific mortality may provide clinical validation on the role of HER2 receptor status for assessment of prognosis and tumour behaviour in patients with DCIS,” they added.