A diagnosis of breast cancer at age 27 is shattering for anyone. But for Eli Oberman, it came with extra layers of anxiety. He is a transgender man, who was born female but began taking male hormones when he was 19 to change gender.

Like many transgender people, Oberman switched gender without having surgery to change his body. The cancer was a stark reminder that he was still vulnerable to illnesses from his original anatomy — and that the medical world has blind spots in its understanding of how to take care of trans men and women.

“I just felt overwhelmed on all levels,” Oberman said. “Overwhelmed about facing the diagnosis, overwhelmed about the irony of it being this part of my body that was already so fraught for me.”

About 1.4 million adults in the United States report they are transgender, according to a recent analysis of federal and state data. That figure is twice the previous estimate, and as awareness has increased, the health care system has begun scrambling to meet their needs.

The government lifted a ban on Medicare coverage for transgender surgery and hormone treatment in 2014, and in 2015 New York state ended a similar ban for Medicaid patients. This year, a rule under the Affordable Care Act banning discrimination in health care specifically included protection for transgender people.

Hospitals and professional schools have begun training employees and students on transgender medicine, and on basic etiquette like addressing trans men and women by the name and pronoun they prefer. At the Mount Sinai Health System in New York, which recently opened a Center for Transgender Medicine and Surgery, about 8,000 employees had such training last year.

“When I think back to the earlier days and think where we are now, it’s unbelievably better,” said Barbara E. Warren, a psychologist and director for LGBT programs and policies at Mount Sinai.

But there are still struggles. Warren and other experts said it was common for transgender people to avoid screenings and other medical care for parts of their bodies associated with their original gender. If problems do arise, they may find themselves in situations like Oberman, who suddenly became the lone male patient in waiting rooms full of women, and a target for curiosity or scorn from some health workers.

Oberman, now 33, was treated for the cancer six years ago, but decided just recently to speak about it publicly in hopes of helping to improve care for others.

He has big, dark eyes, thinning hair, a warm smile and a leafy tattoo wreathing one arm — the kudzu vine, he said, because it is “so unstoppably alive.” He lives in Brooklyn, has a degree in poetry and education, and plays violin in a rock band called the Shondes (“Disgraces,” in Yiddish). His day jobs have included managing a database for a nonprofit organization.

He began taking testosterone when he was 19 for its masculinizing effects — these include increased facial and body hair, a lower voice, more muscle and, usually, an end to periods. But he never had surgery to change his body. Many trans people do not, and so many trans men still have ovaries and vaginas, and trans women, prostate glands and penises.

Early in his transition, Oberman wanted “top surgery” — breast removal — but could not afford it, so he wore binders to flatten his chest. Gradually, he became more comfortable with his body and lost interest in the surgery.

He first noticed a breast lump in 2010. It was not easy to feel, and cancer at his age just didn’t seem possible.

He let six or eight months go by before having scans and a biopsy. Those tests required leaving the safety of his usual clinic, which specialized in LGBT patients, and plunging into the world of mainstream medicine, where he said doctors treated him with respect, but other workers did not.

“I had some horrible experiences,” he said.

During one procedure, when Oberman had his shirt off, a male technician, seeing that he was transgender, exclaimed: “Why would you do this to yourself? It’s disgusting.”

Oberman never reported the episodes.

“I’m not proud to say I didn’t complain,” he said, adding that he wished he had done so for the sake of other patients.

But he was facing a life-threatening disease. The cancer was aggressive. He would need both breasts removed, and then chemotherapy.

“I felt guilty, able to get free surgery I didn’t want because I had cancer, and so many others want it and can’t get it,” he said.

He soon learned that mastectomies, which remove as much breast tissue as possible, differ from top surgery, which preserves enough to give the chest a male-looking contour. Because he had cancer, top surgery was not a safe option: It would leave too much breast tissue, and too much risk of recurrence. Friends who have had top surgery were stunned to find out they still had a risk of breast cancer because of the tissue left behind, he said.

Before surgery, thinking that testosterone might interfere with healing, Oberman’s doctors advised him to stop taking it for a month.

He followed their advice, but soon, he said, “I went insane. I wasn’t rational. I was lying on the floor, crying.”

Back on the hormone, he became himself again.

Chemotherapy gave him a “definitionless moonface,” he said, and it coarsened his features and thinned his hair permanently. It had taken him years to feel comfortable in his trans identity, and now, he said, “It felt like starting all over again.”

He would have liked to join a breast-cancer support group, but feared he would not be accepted.

Oberman said that in “moments of dark paranoia,” he wondered if taking testosterone might have caused his cancer — or if it was unrelated and the tumor might have developed anyway. His mother and her mother had both had breast cancer — though well after menopause.

The hormone question concerns Oberman’s oncologist, Dr. Paula Klein, who specializes in breast cancer at Mount Sinai Beth Israel (not the same hospital where he had his biopsies and surgery). She said trans men with breast cancer were often urged to stop taking testosterone. One reason is that the body converts some testosterone to estrogen, which can speed the growth of many breast tumors. And some breast cancers may also be stimulated by testosterone, she said.

But there is no solid data to guide trans patients, and Oberman does not want to stop taking the hormone.

Klein was an author of a journal article in 2011 about two other trans men with breast cancer. Both took testosterone and, like Oberman, chose to stay on it. Few other cases have been reported.

Klein has been suggesting that Oberman have his ovaries removed. Part of her reasoning was that he had stopped taking tamoxifen, a drug commonly prescribed to prevent breast cancer recurrence. Taking out the ovaries would mean lower estrogen levels, which would help prevent a recurrence of breast cancer.

“You would definitely benefit,” she said during an office visit in September.

“It’s a slam dunk for someone like you, taking away all your female parts,” Klein said, adding, “We thought you’d eat that up. A transgender gift.”

“Except I don’t want it,” Oberman said. He did not want more surgery or the hormonal jolt that removing his ovaries would bring. He thought the mastectomies and chemotherapy had very likely cured him.

Klein backed off, saying, “Look, the odds are that you’re going to be fine.”

He hugged her on the way out. It seemed likely that they would have this conversation again.