By Dr Juliana Ho, Consultant
Department of Diagnostic Imaging, NCC
Screening for any cancer in
general can reduce mortality when the following three criteria are
met:
Prevalence of the disease must be sufficiently large within
a population
The tumour must have a better cure rate at an early stage
Should be detectable by methods that are convenient, cheap
and not harmful to the individual
Breast cancer is the most common
cancer affecting Singapore women with more than 3500 new cases being
diagnosed between 1993-1997. Studies have shown significant reduction
in mortality by 20 to 40% in women above 50 years old due to organized
screening services. Detection of smaller cancers has led to breast
conservation and better prognosis.
Mammography is the most sensitive test for detection of
pre-cancerous breast condition ductal carcinoma-in-situ (DCIS) which
presents as micro-calcifications. The sensitivity of screening mammograms
can be as high as 98% in women over 50 yrs old with fatty breasts
and as low as 84% in younger women with dense breast tissue. The risk
of breast exposure to radiation is acceptably small.
Ultrasound and Magnetic
Resonance Imaging (MRI) have not been able to meet the
criteria stated above for routine screening of individuals without
symptoms.
However, ultrasound is useful
for the evaluation of palpable and mammographic abnormalities, for
preoperative evaluation of disease extent and for the evaluation of
younger women with breast cancer symptoms.
Magnetic Resonance Imaging (MRI)
is highly sensitive in the detection of breast cancer, not limited
by the density of breast tissue and it is also used to evaluate women
with free silicone breast injections, though false-positive results
are common.
With any imaging method, it is essential that suspicious lesions can
be readily localized for either percutaneous or surgical biopsy. Most
benign lesions can be managed without surgery and a specific diagnosis
can be achieved using percutaneous core biopsy. When cancer is detected
definitive treatment can be planned.
In summary, despite ongoing controversies in breast cancer screening,
high quality mammography interpreted by experienced radiologists working
as part of a multidisciplinary team remains the only proven method
of detecting early breast cancer in an asymptomatic population.
For more information on cancer screening, please call the Cancer Helpline
on tel: 622-55-655 or email cancerhelpline@nccs.com.sg
