This Woman's COVID Vaccine Side Effect Led to a Stage 2 Breast Cancer Diagnosis

"As much as COVID sucked-it saved me," Jennifer Mosely said about her cancer diagnosis.

A woman is Iowa is speaking out about an unexpected benefit of the COVID-19 vaccine: Getting the shot resulted in a stage 2 breast cancer diagnosis.

Jennifer Moseley told the Des Moines Register that she noticed a swollen lymph node in her left arm two days after receiving her second dose of the Pfizer vaccine in April. But because the swollen lymph node was in the same arm where she had the vaccine, she didn't think much about it.

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Two days later, the lymph node was still tender. Moseley, who has a family history of breast cancer, realized she hadn't done a breast self-exam in a while. When she did the self-exam, she found a lump the size of a flattened grape in her right breast.

Moseley made an appointment with her doctor to get the lump checked out, which led to a mammogram and a biopsy. Finally, in mid-May, she received a diagnosis: She had stage 2A invasive lobular carcinoma breast cancer, the same cancer that killed her cousin at age 38.

Swollen lymph nodes can be a side effect of the COVID-19 vaccine and other types of vaccines, infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health. Lymph nodes are part of your immune system and they can be activated—and swell—when you're exposed to something like a vaccine, he explains.

"Anything that stimulates your immune system can impact the lymph nodes that are near the injection or infection site," Dr. Adalja says. This vaccine side effect is so common that the Society of Breast Imaging (SBI) issued a warning about it in February, recommending that women wait to schedule a mammogram at least four weeks after their COVID-19 vaccine—so women wouldn't think that swollen lymph nodes from the vaccine were a sign of breast cancer.

Moseley's vaccine didn't cause the lump in her breast, it started a train of thought that motivated her to check herself for signs of cancer. This, Dr. Adalja points out, was a "good coincidence."

Moseley noted that she had a routine mammogram scheduled in July. But if she hadn't been vaccinated in April and discovered the swollen lymph node, her cancer could have grown before it was detected. "The COVID-19 shot, I'm gonna say—as much as COVID sucked—it saved me," she told the Des Moines Register.

Moseley had a double mastectomy and breast reconstruction in mid-June, and is now recovering. Her doctors think they removed all of the cancer, and her family is hopeful that she won't need to undergo chemotherapy.

Moseley is now encouraging people to check their breasts regularly. "Everyone should be aware that they need to examine their breasts more often," she said.

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