Screening for cancer: Is more always better?
SINGAPORE — Hollywood actress Angelina Jolie’s double mastectomy and oophorectomy (ovary removal surgery) to minimise her risks of breast and ovary cancers raised eyebrows and discussions on cancer screening. So did singer-songwriter Taylor Swift’s advocating for early screening since her mother’s cancer diagnosis last month.
While catching and treating cancer in its early stages improves survival outcomes, is Hollywood’s jumping on the cancer-prevention bandwagon causing more anxiety than good?
It might be so in some cases. Take breast cancer, for example. Studies from the United States and Scandinavia have found that at least one-fifth of breast cancers detected via screening tests are over-diagnosed, said Dr Crystal Ng, medical director of Executive Health Screeners at Parkway Shenton.
An over-diagnosis is when a screening test detects small tumours that might never have progressed to cause symptoms or death in a person’s lifetime, said Dr Ng.
“The over-screening and over-diagnosis of cancer can expose a woman to the risks of cancer treatments. They include surgical deformity or toxicity from radiation, hormone and chemotherapy, as well as the late effects of radiation,” she said.
An over-diagnosis may also occur when other screening tools such as ultrasound and tumour markers (blood test screening) are used indiscriminately, said Associate Professor Philip Iau, senior consultant at Division of Surgical Oncology (Breast Surgery) at National University Cancer Institute, Singapore (NCIS).
According to Assoc Prof Iau, an ultrasound should be used in breast cancer screening only when a physical examination or mammogram picks up something abnormal.
“Ultrasound should not be used as a first-line screening tool for breast cancer. Ultrasound is over-sensitive and may pick out masses that can be indistinguishable from cancer, even in normal breasts.
“This leads to over-biopsy, anxiety and often, insurance discrimination”, said Assoc Prof Iau.
FALSE ALARMS
Then, there’s the issue of false-positive results. This happens when a test shows that a disease is present, even though it is not.
Said Dr Ng: “Such test results can cause anxiety, and are usually followed by additional tests and procedures that can potentially harm the patient.”
At the National Cancer Centre Singapore (NCCS), Associate Professor Koo Wen Hsin, senior consultant at the Division of Medical Oncology, has encountered patients who were referred to the centre because their blood tests showed high levels of CA 19.9, a tumour marker for pancreatic cancer.
However, Assoc Prof Koo noted, other non-cancer conditions, including infection or inflammation in the gastrointestinal tract, liver, gall bladder and pancreas, can also lead to higher levels of CA 19.9.
Said Assoc Prof Koo: “These patients have gone for extensive endoscopy, CT scans and MRI scans. None of them had cancers. All stopped checking after several years but the fear lingered.”
Another anxiety-inducing example is the use of tumour marker CA 125 to screen for ovarian cancer in women who have no symptoms. This test is often included as part of executive-health screening packages, said Associate Professor A Ilancheran, senior consultant at Division of Gynaecologic Oncology at NCIS.
Routine screening for ovarian cancer in the average-risk population is discouraged because there is currently no effective screening strategy for it, said Associate Professor Jeffrey Low, head and senior consultant of the Division of Gynaecologic Oncology at NCIS.
According to Assoc Prof Ilancheran, professional gynaecologic oncology societies have specifically recommended that CA 125 not be used for ovarian-cancer screening in women with no symptoms.
Assoc Prof Low explained that tumour markers like CA 125 are not specific enough. The test can show elevated levels even when there is no cancer, because of conditions such as menstruation and ovulation.
“However, the test may also indicate normal levels in half of early-stage ovarian cancer cases. Therefore, an elevated CA 125 is usually a false alarm but a normal CA 125 is not reassuring either,” he said.
Tumour markers are substances that are made by cancer cells. However, they can also be produced by normal cells in the body in response to non-cancerous conditions, although they are produced at much higher levels when there is cancer, said Dr Ng.
“Not everyone with a particular type of cancer will have a higher level of tumour marker associated with that cancer. Moreover, tumour markers have not been identified for every type of cancer,” she said.
Even so, that does not mean these tests do not pick up cancers, said Assoc Prof Koo.
Dr Ng recalled a woman who had insisted on including all available tests for tumour markers in a health check package for her parents, who were in their 50s.
“She wanted peace of mind although her parents did not have any significant family history and medical concerns. Her father’s tumour marker alpha fetoprotein was at an exceedingly high level. We got the family back to do further diagnostic tests and confirmed it was liver cancer,” said Dr Ng.
Sometimes, MORE IS BETTER
For colorectal cancer, early screening is always better even when there is no family history of the cancer, said Dr Cheong Wai Kit, senior consultant at the Division of Surgical Oncology (Colorectal Surgery) at NCIS.
“Screening detects polyps that must be removed before they turn malignant. The earlier the stage of the colorectal cancer detected and treated, the higher the chance of survival.
However, this screening is presently underutilised in Singapore,” said Dr Cheong. The same goes for cervical cancer, which is the most preventable cancer and fulfils the World Health Organization (WHO) criteria for screening and prevention, said Assoc Prof Low.
Said Dr Ida Ismail Pratt, associate consultant at the Division of Gynaecologic Oncology at NCIS: “Cervical cancer is the only cancer that can be effectively screened to stop the disease from developing all together. This is the only cancer where the cause is known (due to the human papillomavirus) and can be detected with a Pap smear — a sensitive, easy-to-use test. The precancerous stage is also easily treated before cancer develops.”
She recommended women aged 25 to 69 years old, who have had sexual activity, to go for regular Pap smears every three years.
Whether a person should consider screening beyond the recommended basics (see tables on left) also depends on his/her individual risk factors.
“For the general population with no risk factors, basic screening tests that are inexpensive and low-risk will do. For those who have high-risk factors like a strong family history or existing illness linked to cancer, more sophisticated, costly and invasive tests are recommended,” said Assoc Prof Koo.
It is best to speak to your family doctor, who can advise you on the screening tests to go for based on your risk profile, said Dr Ng.
WHICH CANCER SCREENING TESTS SHOULD YOU CONSIDER?
Dr Crystal Ng, medical director of Executive Health Screeners at Parkway Shenton shares the various types. Consult your doctor for further advice.
Type 1: Basic screening tests
Screening test: Faecal immunochemical test
To screen for: Colorectal cancer
Recommended for: 50 years and above
Screening frequency: Once a year
Screening test: Colonoscopy
To screen for: Colorectal cancer
Recommended for: 50 years and above
Screening frequency: Once every 10 years
Additional tests for women
Screening test: Pap smear
To screen for: Cervical cancer
Recommended for: Women aged 25-69 years, who have had sexual intercourse
Screening frequency: Once every three years
Screening test: Mammogram
To screen for: Breast cancer
Recommended for: Women aged 50 to 69 years
Screening frequency: Once every two years
Type 2: Screening tests recommended for high-risk groups
The decision to screen is made on an individual level, based on the person’s risk factors such as family history of hereditary or chronic diseases, as well as exposure to factors that can lead to disease such as smoking.
To screen for: Colorectal cancer
Screening test: Computed Tomography (CT) Colonography
Who should be screened: Above 50 years, not going for screening colonoscopy or FIT (Faecal Immunochemcial Test)
Screening frequency: Once every 5 years if the initial screening with CT colonography is negative. Otherwise, as advised by your doctor.
To screen for: Liver cancer/Hepatocellular carcinoma (HCC)
Screening test: Alpha-FoetoProtein (AFP) and Ultrasound Hepatobiliary System
Who should be screened: Hepatitis B carriers and those with liver cirrhosis
Screening frequency: Once a year for each test
To screen for: Nasopharyngeal carcinoma (NPC)
Screening test: Nasoscopy and tumor marker for NPC
Who should be screened: Individuals with a strong family history of NPC
Screening frequency: As advised by your doctor
To screen for: Prostate cancer
Screening test: Prostate-Specific Antigen (PSA)
Who should be screened: Men aged 50 to 75 years old and those with a strong family history of prostate cancer
Screening frequency: Once a year or as advised by your doctor
To screen for: Breast cancer
Screening test: Magnetic Resonance Imaging (MRI) Breast
Who should be screened: BRCA carriers
Screening frequency: Once a year
To screen for: Ovarian cancer
Screening test: Transvaginal Ultrasound
Who should be screened: BRCA carriers and women at high risk of BRCA mutation
Screening frequency: As advised by your doctor
