It’s already hard enough for blood cancer patients to find a match through the international bone marrow registry, which pairs patients with potential donors who have the right type of tissue. But if you’re Black and Jewish?

For people with multiple ethnic backgrounds who need marrow or stem cell transplants, matching is even harder.

“I remember the doctor saying something like if he was an Irish white boy from Ireland, he might have a better chance,” Monika Clark said about her son, 24-year-old Jordan Jackson-Clark of Oakland.

Jackson-Clark, whom his mom describes as “mixed ethnicity and biracial,” is likely to need a bone marrow transplant after a diagnosis of leukemia two weeks ago.

“It was so out of the blue,” Clark said. “It was so unexpected.”

Jackson-Clark had experienced a few bouts of intense stomach pain over the past summer, one strong enough to send him to the ER. Clark was concerned, but she was never expecting the recent call that they got from the doctor.

Through tears, Clark described the blow of hearing the diagnosis for her son, a Berkeley High School grad who was a camp counselor at the East Bay JCC and a member of the Jewish fraternity AEPi.

“He’s just a gentle, loving young man,” she said.

Jackson-Clark has acute myeloid leukemia, a cancer of the blood and bone marrow. He’s in the hospital getting chemotherapy for the next few weeks. In the meantime, knowing how difficult it will be to find a match for her son, Clark is desperately trying to get the word out about the bone marrow registry.

“Please step out and do something very simple to save a life,” she said.

The ethnic background of a cancer patient who needs a transplant matters, because the markers used to match a donor and patient are inherited. Having the same markers as a donor makes it a lot more likely that the patient’s body will accept the life-saving bone marrow or stem cells.

But the makeup of the database of potential donors is mostly white. “For people of color and mixed race, the percentage of matches is 23 percent, and for white Caucasians it’s 77 percent,” Clark said.

According to the nonprofit Gift of Life, while more than 12 percent of the American population is Black, only 4 percent on the registry are, and the percentages are similarly out of proportion for other ethnic groups.

Gift of Life was founded by Jay Feinberg, who was diagnosed with leukemia more than 20 years ago and needed a bone marrow transplant from a white Ashkenazi Jew. He sought a donor match, but at that time the database was sorely lacking in diversity. Efforts since then by his organization and others have greatly increased ethnic representation in the registry, but matches for mixed-ethnicity patients remain scarce. Jackson-Clark has the best chance of being matched with another person who is Black, white and Ashkenazi, but there simply aren’t many in the database.

The solution is getting more potential donors into the system. Clark is asking people to get tested with a simple cheek swab through Be the Match or any other registration service — not only if they think they might be a match for her son, but also for all of the other patients out there who need matches. Optimal donor ages are 18 to 44; registration is free and can be done through the mail. That puts them on the international registry of potential donors, and the more people who are on the list, the more likely it is that they could be a match for a cancer patient.

That’s why Rabbi Yigal Rosenberg of Chabad of Santa Clara held a registration drive in February and encouraged young people to get on the list. When he got a call from Gift of Life a few days later, he thought it had something to do with the event.

“They said, actually, you are a match!” he said.

Rosenberg had the right kind of stem cells to help a 40-year-old man based on a swab he’d given 10 years previously in New Jersey. (Whether marrow or stem cells are donated depends on the patient’s treatment needs.)

“I’m like, what are the chances?” Rosenberg said. “Literally I just hosted an event two days ago!”

He immediately said yes and began a required series of injections to boost stem-cell production — checking with another rabbi to make sure it was OK to have the shots on Shabbat as well.

“This is the one thing you’re allowed to compromise on, in Shabbat observance, is to save a life,” he said.

Then, at the beginning of September, he drove down to San Bernardino, where he was put up in a hotel. He spent one day at the donation center attached to a machine that pumped blood out, filtered out and collected the stem cells, and returned the blood to his body. Rosenberg said the experience wasn’t difficult at all.

“I just felt so empowered during the entire process,” he said.

He even livestreamed it on Facebook as a way to encourage more registrations, and to dispel some of the fear around donation. (Whether a patient requires the donor’s marrow or stem cells depends on the particular treatment protocol.)

“I went right back to the hotel, jumped in the Jacuzzi for a bit and took a nap,” he said. The next day he was back on his way to Santa Clara to resume his duties.

Clark, a former JCC preschool teacher, said it is important for people to know that donating stem cells and even bone marrow is not as intrusive or painful as it used to be. And anyone on the registry can always decide later that they’re not ready to donate, so getting the swab does not commit them to doing so.

“The greatest Rosh Hashanah gift from the Jewish and biracial communities would be to spread the word far and wide with your communities, and to please get on the donor list by sending away for a simple and free cheek swab,” she said. “You just might save my or someone else’s child’s life.”