Some images on the mammogram may look like cancer but may not be cancerous.
False positives lead to further invasive and potentially harmful investigations such as biopsy, as well as emotional stress.
Sampling errors may also occur during biopsies. Even if the biopsy shows no serious lesions, it could just be a sampling error, in that the biopsy needle missed the real cancer cells.
Patients would still be required to go for another mammogram in a few months.
Missed cancer, reported to be in the range of 10 per cent to 30 per cent in breast cancer screenings, is another potential problem.
In short, abnormal mammogram results do not necessarily mean the presence of breast cancer, while a normal mammogram report does not completely exclude the presence of the disease.
The harms of cancer screening ought to be balanced by its benefits.
For breast cancer, most experts agree that screening mammograms bring more benefits than harm.
Indeed, cancer screening is a complex science.
To date, public cancer screening is recommended only for breast, prostate, colorectal and cervical cancer. Major cancer guidelines also differ in their screening details, namely age of starting and stopping the screening programme, as well as the interval duration of surveillance.
I strongly urge the public to consult their family doctors before and after cancer screening.
Desmond Wai Chun Tao (Dr)