MONTREAL -- When it comes to COVID-19 vaccines there's been so much to wrap our heads around, and that includes the need to constantly consult our calendars.

When can I sign up? When can I get my second dose? How many weeks delay is that?

But now that the campaign is picking up speed in Quebec, some Montreal doctors want to make sure women know there’s also a timing issue when it comes to getting the vaccine and scheduling a routine mammogram.

The Canadian Association of Radiologists advises women to schedule their regular screening mammogram either before they get a dose of the vaccine or six weeks afterward.

“I think the word is slowly getting out there,” said Dr. Gabrielle Cassir, an obstetrician-gynecologist at St-Mary’s Hospital in Montreal.

She hears from patients that when they call a clinic to make an appointment, the receptionist now asks them when they got their vaccine, Cassir said.

But that has caused some concern, she said, with “patients wondering why they are asking me this question, what should I be doing?”

FALSE POSITIVES

A few months ago specialists observed that particularly with the mRNA Pfizer and Moderna products, the vaccines can cause swelling in the lymph nodes under the arm that received the injection.

“It is a very common reaction to have a temporary enlargement of lymph nodes, a common immune response to the vaccine,” Cassir said, though it doesn’t happen to everyone.

But if the lymph nodes do swell post-vaccine and sore lumps develop under the arm, it can create a “confusing picture,” says St. Mary’s Hospital radiologist Dr. Sagi Kaduri who regularly interprets mammogram results.

“In the case where the lymph nodes are enlarged, we would see them on the image as being like a small mass basically in the area of the armpit. It does stand out to you visually right away,” Kadoury said.

If the radiologist doesn’t know the patient was recently vaccinated, they would consider the swelling a concerning finding that warrants further investigation, and patients would be referred to their family doctor for an ultrasound, or even a more invasive procedure.

Earlier this spring, experts at Duke University School of Medicine in the United States heard about women who were undergoing unnecessary biopsies as a result, and they stepped in to advocate on their behalf.

“So getting the word out is [important] to try and really avoid unnecessary callbacks, tests, anxiety, and stress,” said Cassir, especially when the situation can be easily managed with proper scheduling.

Even knowing ahead of time that the woman having a screening mammogram got a vaccine a short time before the mammogram can create unwarranted concern.

“You could consider that the lymph nodes may be secondary to the vaccine, but you don't know 100 per cent that that's the case,” Kaduri said, adding “it does happen to colleagues,” who then have to ensure proper follow-up.

Both doctors emphasize a woman should not delay getting a diagnostic assessment for any possible breast cancer symptoms that need investigating regardless of the timing of a COVID-19 vaccine.

A complete list of breast cancer symptoms can be found on the Canadian Cancer Society’s website and include a lump in the armpit, changes in the shape or size of the breast, and changes to the nipple.

WHAT IF SOMEONE HAS OR HAD CANCER?

If someone is eligible to get a COVID-19 vaccine but has already been diagnosed with breast cancer, melanoma, or any cancer that can spread to the axilla (armpit), Kaduri says it’s a good idea to get the vaccine in the arm on the unaffected side of the body - again just to prevent any confusion.

The other option suggested by the Canadian Association of radiologists is to choose to get the vaccine injected into the thigh.

Cassir said it’s “an important discussion to have,” with her routine gynecology patients during this still unusual pandemic time when every day brings new science and sometimes new stress.