Why you should care

Carlos Castro-González’s invention is noninvasive and could lead to smoother, more personalized chemotherapy.

Cancer patients undergoing chemotherapy check into a treatment center about every three weeks. They sit in a room alongside other patients, an IV needle dripping medicine into their veins, often for several hours. Cancer is certainly bad news. But the treatment that 650,000 cancer patients in the U.S. undergo each year, chemotherapy, is no picnic either.

While chemotherapy destroys cancer cells, it also attacks the white blood cells that keep our immune systems strong, leaving patients vulnerable to febrile neutropenia — a fever and usually other symptoms of infection. Getting sicker in the middle of chemotherapy not only interrupts treatment but can also be fatal. So throughout chemo, doctors closely monitor patients’ white blood cell levels, typically through needle-based blood tests.

A 33-year-old MIT biomedical engineer named Carlos Castro-González wants to alleviate at least some of the pain. Castro-González is the creator of Leuko — short for “leukocyte,” the scientific name for white blood cells. The device allows patients to monitor white blood cell levels from home, simply by shining a tiny microscope over a fingernail. Leuko, a prototype of which entered a trial with chemo patients in September, uses the microscope’s video footage of blood flowing through capillaries in the nailbed to calculate a patient’s cell count. Ephraim Hochberg, a hematologist-oncologist at Massachusetts General Hospital who advised the Leuko team, says it “has a potentially revolutionary impact.” Pamela Becker, a hematologist at the Seattle Cancer Care Alliance, says Leuko could “improve quality of life and facilitate patient care,” allowing doctors to act faster. “We spend much of our day to just find out the neutrophil count,” she says.

The device is part of the booming telemedicine industry; today, patients and caregivers can increasingly perform some of the tasks at home that once required a trek to the hospital, from cognitive rehab to ECG monitoring. Those footslogs are particularly cumbersome for chemo patients, who can only receive treatments if white blood cell counts are acceptable. Often, they arrive at the hospital only to be sent home. Eventually, Leuko will send white blood cell counts to doctors remotely, saving that psychologically and physically exhausting journey.

Castro-González makes a subdued impression. Skyping from his office at MIT, he looks the part of an introverted, disheveled engineer with swarthy features, thick-rimmed glasses and a wiry frame. Growing up in Leon, Spain, Castro-González was drawn to the cosmic questions of physics. But seeking financial stability, he studied telecommunications engineering at the Technical University of Madrid instead. The field didn’t move him; he returned to his alma mater to earn a Ph.D. in biomedical imaging.

One day, he imagines it could diagnose infectious diseases in the developing world.


Around the same time, Castro-González read Hopscotch, a novel by Argentinian author Julio Cortázar that was written and set in Paris; it kindled in him a fascination with expatriate life. Carlos-González headed to the U.S in 2013 for a postdoctoral fellowship from the Madrid–MIT M+Visión Consortium, which helps Spanish engineers launch biomedical ventures at MIT. Just a few months before, he received sobering news: His roommate had been diagnosed with non-Hodgkin’s lymphoma, a blood cancer. Luckily, doctors caught it early. But he watched his friend undergo chemotherapy, lose his hair and isolate himself, fearing infection. “It really exposed me to the problems these patients suffer,” he says.

By early 2014, he came upon the idea of an at-home device to minimize hospital trips. His initial team — two engineers and a physician — conceived of a finger-prick test before realizing regulatory agencies hadn’t approved these devices for home use, due to the technical skill needed to get an accurate reading. Back at the drawing board, Alvaro Sánchez-Ferro, the physician, suggested using capillaroscopy, a technique that requires holding a tiny microscope over the fingernail. Meanwhile, the team began thinking about the blue field entoptic phenomenon, otherwise known as the cluster of tiny, spiraling dots you might see while gazing at a sunny sky. Those dots? They’re white blood cells flowing through the capillaries in front of your retina. Since they’re more transparent to blue light than red blood cells, we see them as clear dots. Castro-González had an idea: bring that sunny sky to your fingernail, imaging white blood cells with a microscope and blue light.

Today, as the prototype is tested, the hope is that Leuko receives FDA approval in under five years, says Castro-González, named one of MIT Technology Review’s Innovators Under 35 in 2015. One day, he imagines, it could diagnose infectious diseases in the developing world.

But Leuko can’t yet distinguish between various white blood cells. Until then, “its use among patients undergoing chemotherapy would be limited,” says Mikkael Sekeres, a hematologist-oncologist at the Cleveland Clinic. An oncologist would prescribe antibiotics or adjust a chemo dose in response to a low count of neutrophils (which play a central role in fighting infection), for instance, but maybe not other white blood cell types.

Emails from patients and their families invigorate Castro-González. A few weeks ago, a father wrote about his son, who has leukemia and was neutropenic — again. The father is monitoring Tommy’s temperature closely, he said, checking when an ER visit is necessary. A Google search led the parents to Leuko. “If you have devices for field testing, then please consider us,” he wrote.

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