SINGAPORE - Patients who have recently taken the Covid-19 vaccine are advised to reschedule their yearly mammogram screenings as the presence of swollen lymph nodes, which is one of the known side effects of the jab, could be mistakenly identified as a sign of breast cancer.
Doctors have advised them to move their mammogram screenings to either before receiving their Covid-19 vaccine or a few weeks after their second dose, to avoid confusion.
The Pfizer-BioNTech vaccine can cause swollen lymph nodes on the neck or arms, though it usually gets better by itself in a week or so, according to the Ministry of Health.
Dr Tan Yah Yuen, a breast surgeon at the Mount Elizabeth Hospital, said the recent Covid-19 vaccination may cause swollen underarm lymph nodes on the vaccinated arm, which could lead doctors to "falsely suspect" an early sign of cancer.
"If the clinical suspicion is that the swollen lymph node is due to the vaccination and not breast cancer, then a repeat ultrasound can be done in two to three months to follow up on the swollen lymph nodes for resolution," she added.
So far, she has seen two patients, both healthcare workers, who had their mammogram and ultrasound screenings after receiving their Covid-19 vaccinations.
Both had enlarged lymph nodes on their underarm where the jab was given.
Since there were no other "suspicious signs" of breast cancer, the hospital will follow up with a repeat ultrasound.
All other patients who just received their Covid-19 vaccinations have been informed to reschedule their check-ups, said Dr Tan, noting that the American Society of Breast Surgeons has recommended that women should consider scheduling mammogram or ultrasound checks before taking the first vaccine dose, or four to six weeks after the second dose.
Women who are in cancer remission should also discuss with their doctor the appropriateness of rescheduling their mammogram or ultrasound checks, and they should seek to have their vaccine jab on the opposite arm if possible to avoid false alarms of cancer recurrence, she advised.
Dr Ong Kong Wee, medical director of K W Ong Breast and General Surgery Clinic, said the concern over enlarged or swollen lymph nodes in the underarm is that it could be a sign of breast cancer spreading to the lymph nodes.
But this could also be due to infection or autoimmune diseases.
He also advised patients to schedule their mammogram screenings before going for their vaccine as this would prevent them from being subjected to more "extensive and invasive tests", such as a needle biopsy.
Agreeing, infectious diseases expert Paul Tambyah, who is also president of the Asia Pacific Society of Clinical Microbiology and Infection, said that it would be prudent to schedule mammograms at least two weeks after receiving the vaccine, or before the vaccination to "avoid unnecessary anxiety".
He added that the Pfizer-BioNTech vaccine trial found that there were 64 cases of swollen lymph nodes among the vaccine recipients, versus six cases who had received the placebo. Both groups had more than 20,000 people each.
The report from the US Centres for Disease Control and Prevention on the international trial had also stated that the lymph node swelling lasted an average of 10 days, added Prof Tambyah.
However, he noted that the trial recipients were not specifically asked if they had experienced lymph node swelling, so the figures from the trial might be under reported.
On the other hand, results from the Moderna vaccine trial conducted in the US had found that 14 per cent, or 2,090 of the 14,677 vaccine recipients had developed swollen lymph nodes, against 3.9 per cent of the placebo recipients. These typically lasted for around seven days after the vaccination.
Professor Dale Fisher, a senior infectious diseases specialist at the National University Hospital, said it would not be surprising to find swollen lymph nodes after a vaccine jab as it is a major site for the body's immune response. He also advised separating both medical procedures, where possible, in case one affects the other.