Hong Kong Academy of Medicine. CC BY-NC-ND 4.0
EDITORIAL
Breast cancer screening—towards a broader
coverage of the general population
CY Lui, FHKCR, FHKAM (Radiology)1; Julian CY Fong, FHKCR, FHKAM (Radiology)1; Martin CS Wong, MD, MPH2,3
1 Hong Kong Women’s Imaging Limited, Hong Kong
2 Jockey Club School of Public Health and Primary Care, The Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong
3 Editor-in-Chief, Hong Kong Medical Journal
Corresponding author: Dr CY Lui (cylui@hkwi.com.hk)
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The primary purpose of breast cancer screening is
to detect breast cancer earlier at an asymptomatic
stage hopefully before it becomes more advanced
or metastasised, which is the major cause of patient
death. The breast cancer detected under screening
are usually smaller in size with better prognosis,1 2
and patients can therefore benefit from less extensive
surgical treatment with fewer complications such
as lymphoedema. It may also reduce morbidity
secondary to the use of systematic chemotherapy,
and lower its recurrence rate
In 2021, the Cancer Expert Working Group on
Cancer Prevention and Screening (CEWG) updated
its recommendations on breast cancer screening
for the female general population of Hong Kong.
Women with certain combinations of risk factors
are recommended to consider mammography
screening every 2 years.3 Addressing the rising
breast cancer incidence in Hong Kong, the updated
recommendation is a big leap forward compared
to the previous version which only mentioned
‘insufficient scientific evidence to recommend or
against mammography screening’.
The benefits of mammography have been
widely reported in Western populations.4 However,
whether studies from Western populations are
directly applicable in Chinese populations remains
controversial, primarily because this population
generally has denser breast tissue and difference
in incidence. In this respect, a 10-year study
conducted in Taiwan, involving over 1.4 million
women of mainly Chinese ethnicity, found that
universal biennial mammography was associated
with reduction of mortality by 41% and stage II+
breast cancer by 30%, compared with annual clinical
breast examination.5 In Hong Kong, Lui et al6
found that the crude cancer detection rate of an
opportunistic screening programme was five per
1000 mammograms performed. Experience from
Hong Kong Breast Cancer Foundation found a
detection rate of 7.5 per 1000 asymptomatic women
screened.7 These data suggested that mammography
screening is useful to detect breast cancers in Hong
Kong.
Potential risks of breast screening have also
been overstated, including overdiagnosis and overtreatment of ductal carcinoma in situ (DCIS)
detected by mammography screening. However,
Duffy et al8 studied over 5 million women screened
in the United Kingdom for four consecutive yearly
screening rounds, and showed that there was a
significant negative association between detection of
DCIS at screening and invasive interval cancers. For
every three screen-detected DCIS, there was one less
invasive interval cancer over the next 3 years. These
results indicate that early detection of DCIS and
subsequent treatment is worthwhile in prevention of
future invasive diseases.
Another risk that is often overstated is the
effect of screening causing anxiety among patients.
Anxiety in patients who received breast cancer
screening tends to be short-term, and these women
have a high tolerance for false positive results.9 10 11
Findings from the longitudinal DMIST (Digital
Mammographic Imaging Screening Trial) showed
that the anxiety associated with false positive
mammogram was only transient with no measurable
health utility decrement, yet it increased women’s
intention to undergo future breast cancer screening.12
Although there is potential for false positive results
to cause anxiety and lead to unnecessary biopsy and
treatment, the situation can be much alleviated with
updated technology and quality assurance by experts
with adequate experience in breast screening.
Bilateral two-view full-field digital
mammography is currently the standard of screening
mammography. With technological advancements,
digital breast tomosynthesis (DBT), also known as
3D mammogram, has become more widely used.
Friedewald et al13 found that DBT was associated
with a 41% increase in invasive cancer detection,
49% increase in positive predictive value for recall,
21% increase in positive predictive value for biopsy,
and 15% reduction of overall number of recalls.
Older studies reported that the radiation dose
of DBT was much higher than that of conventional
two-dimensional (2D) digital mammography.
However, these studies often compared the
radiation dose between “DBT combined with digital
mammography” and “digital mammography only”.
Using newer DBT technology with synthesised 2D
mammogram capacity without separate scanning for 2D images, the radiation dose of DBT is comparable
to that of conventional 2D digital mammography—and just less than half of the United States Food
and Drug Administration Mammography Quality
Standards Act dose limit for mammography.14
And with the use of DBT, it is associated with
fewer additional radiation exposure from recall for
additional cone compression view. This newer DBT
technology is now widely available in Hong Kong.
To implement a successful breast cancer
screening programme in Hong Kong, modern
hardware and manpower readiness are equally
important. The imaging centre should have
mammography machines, radiographers, and
radiologists that meet the standards recommended
by Hong Kong College of Radiologists.15 Quality
assurance, including regular auditing of the
programme’s performance should be in place.
Multidisciplinary meetings with radiologists,
surgeons, pathologists, and oncologists working in
as a team should be held regularly to discuss relevant
cases and to facilitate further investigations or
treatment plans. There should also be administrative
support to follow up on screening and biopsy
results, and provide timely arrangement of further
investigation or treatment if cancer is suspected
or confirmed. A system should be implemented
to remind patients to attend the next screening
appointment.
To prepare for large-scale breast cancer
screening, forward planning is essential, such as
training of an adequate number of mammographers,
radiologists with a special interest in breast
screening, and breast surgeons specialised in early
breast cancer surgery and treatment.
Whereas the risks of screening are frequently
discussed, the harms of not screening are often
overlooked. Those women not attending screening
are associated with development of a significantly
larger tumour, a more advanced stage of disease at
diagnosis, poorer prognosis, lower survival rate,
and higher recurrence rate. There is also a higher
cost and extent of treatment, especially if there is a
need for chemotherapy for advanced disease. It has
been estimated that the cost of treating advanced
metastatic breast cancer exceeds US$250 000 per
patient, and the average cost of treating advanced
cancer in the first year after diagnosis is almost
double that of early cancers.16 In addition to the
cost for treatment, there are extra societal costs,
including productivity loss and staff turnover, as
well as the time and expenses of the caretakers of the
patients.
The relatively dense breast tissue among
Chinese women not only impairs the performance
and resulting benefits of mammography, but also
is an independent risk factor for breast cancer. The
technology of DBT, supplemented by ultrasound or magnetic resonance imaging (MRI), may be used to
enhance the sensitivity for detecting cancer. Whereas
supplementary ultrasound is widely used because of
its easy availability, a recent study found that contrast
enhanced MRI provides the greatest increase in
cancer detection and reduce interval cancers and
late-stage disease.17 The abbreviated MRI technique
will reduce the cost and improve the availability of
this technology. It is hoped that the CEWG may take
this newer evidence into consideration in its next
update.
With the updated recommendation of CEWG
on risk-based screening, and the experience of
opportunistic mammography screening in Hong
Kong since 1993,6 we believe that Hong Kong should
have the capability and expertise to organise quality,
population-based screening similar to other Asian
countries and cities. Because breast screening is
a primary care activity, we anticipate that district
health centres may play a crucial role to enhance
awareness and promote its implementation in the
community as one of their key roles and functions.
We are confident that the findings from evaluation
of the Breast Cancer Screening Pilot Programme
started on 6 September 2021 could further inform
policy formulation.
Author contributions
All authors contributed to the editorial, approved the final
version for publication, and take responsibility for its accuracy
and integrity.
Conflicts of interest
The authors have declared no conflict of interest.
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