When Andy Provencher crashed his mountain bike and tumbled over the handlebars, he thought his wife's reaction would be his biggest problem.

It was June 2020, when COVID-19 was soaring nationwide. The emergency room was "the last place that she wants me to be," Provencher said. The father of three had several broken bones and a punctured lung. But doctors spotted something even more alarming.

"The emergency room doctor said, 'We've done some scans, we've seen in your lungs, and your lungs are littered with masses. This looks like a very aggressive form of lung cancer,'" Provencher recalled.

The startling conversation spurred a year-long search for answers. Provencher would get a diagnosis one day and have it contradicted the next. Multiple doctors thought Provencher had terminal lung cancer, but tests and biopsies were inconclusive.

"We went to every doctor there was. I went to my PCP, I went to a hematologist, a pulmonologist, a rheumatologist. And we never really had like a solid answer, a solid diagnosis," Provencher, 45, recalled.

Meanwhile, he was losing energy, struggling to walk up stairs and aching so much that he moved "like a 90-year-old man." Provencher was advised to begin chemotherapy.

Two weeks before beginning the aggressive treatment, Provencher saw a physician's assistant who was studying rheumatology. They had just learned about a rare condition called IgG4-RD, and thought it fit Provencher's symptoms. Provencher quickly booked an appointment with Dr. John Stone, a rheumatologist and one of the premier experts on IgG4-RD. After a few tests, Stone finally gave the father of three a diagnosis — and a plan.

"Ever since I went over the handlebars, our world really started spinning, and for that diagnostic year, it just began to spin faster and faster and faster. Once I heard that from Dr. Stone, our world stopped spinning," Provencher said. "It's like in 'The Wizard of Oz,' when the house sits on the ground. You can breathe."

What is IgG4-RD?

IgG4-RD is a rare immune condition that can cause lesions, inflammation and scarring in "virtually any organ system," said Dr. Ambreesh Chawla, a rheumatologist at the Cleveland Clinic. It most often affects the pancreas, liver and biliary tree, salivary glands and lymph nodes, Chawla said, but can also affect the lungs, eyes, central nervous system and more. The condition has a wide range of symptoms depending on which organs it affects and how severe it is.

Stone said IgG4-RD moves slowly and often damages organs before a patient even knows something is wrong.

The condition also can't be determined from a blood test or biopsy, and doctors need to rule out other illnesses before they confirm a person has IgG4-RD, Chawla said. Stone said it's typical for a patient to wait years for a diagnosis, and that an "astonishing" number of patients are misdiagnosed at first.

"Unfortunately, Andy's story of delayed diagnosis is the rule rather than the exception," said Stone, who is also a professor of medicine at Harvard Medical School and the Edward A. Fox Chair in Medicine at Massachusetts General Hospital.

Provencher's incorrect diagnosis of terminal lung cancer had taken an "enormous mental toll," Stone said.

"He had multiple large nodules in both lungs. While this was bad enough, his mental status was even worse," Stone said.

A first-of-its-kind trial

Stone enrolled Provencher in a clinical trial designed to see if a medication called inebilizumab would be effective in treating IgG4-RD. Inebilizumab is a monoclonal antibody that targets CD19, an antigen found only on the surface of the immune system's B cells, in a process called B cell depletion.

In the first phase of the trial, some patients received inebilizumab and steroids, while a control group only got steroids. Stone had prescribed B-cell depleting agents and steroids as off-label IgG4-RD therapies for about 15 years, but this trial could lead to the Food and Drug Administration's first-ever approval of a medication to treat the condition.

During the year-long first phase of the trial, Provencher wasn't sure which treatment course he was receiving, but suspected he was in the control group. In the second stage, both Provencher and Stone knew he was receiving inebilizumab. Provencher began to see a "wonderful" improvement.

Stone said that the patients who received inebilizumab had their risk of a disease flare over one year reduced by 87%. Also, 90% of the patients who received inebilizumab were able to discontinue steroid treatment for at least one year, compared to 37% of patients who were treated with only steroids. In April 2025, inebilizumab became the first FDA-approved IgG4-RD treatment.

"Keep moving forward"

Three years after his diagnosis, Provencher is continuing to take inebilizumab and is feeling great. He has the energy to play with his kids and go out with friends.

However, the damage caused before his diagnosis will last. IgG4-RD can go into remission, but has no permanent cure, Chawla said. Provencher said he hopes the treatment will help him avoid a relapse and keep the disease from progressing further.

"Certainly I have my struggles from day to day, with a little exhaustion and whatnot, and some other symptoms, but the medicine has put me in a decent place right now," Provencher said.

In 2023, Stone founded the IgG4ward! Foundation, which works to educate patients and connect them with resources. Stone asked Provencher's wife, Katharine, to be its director of advocacy and community engagement. She accepted. Provencher said he hopes further advocacy and education about the disease can lead to a better diagnostic process.

"I think about the what-ifs all the time, and I think that my symptoms would have gotten more and more extreme, to the point where I would have hopefully came to the same place, but with more damage," Provencher said. "The most important thing is just keep going. Keep asking questions, keep moving forward."

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