The Virologist Who Stopped Her Own Cancer With Viruses

The experiment begins the moment a needle punctures a dark, firm tumor and releases millions of viruses inside. The story Kurzgesagt tells centers on virologist Beata Halassy of Croatia, who in the summer of 2020 faced a recurrence at her mastectomy site and decided, with colleagues closely monitoring her, to inject viruses she had grown herself directly into the mass.

Her history explains the choice. First diagnosed with breast cancer in 2016, she had surgery to remove the bulk of disease and then four cycles of harsh chemotherapy to mop up residual cells. A local recurrence in 2018 was excised, yet the disease returned again as a larger, more aggressive mass invading muscle and skin, classified as stage 3B and carrying a slim chance of long-term survival if left to spread.

Instead of starting another round of chemotherapy, Halassy chose to keep her immune system intact. Leading a research unit at the University of Zagreb and skilled in cultivating and purifying viruses, she knew that a suppressed immune system would undermine virotherapy, whose main killing power comes from the host response. The plan was to prepare the agents herself and use them to call her own defenses to the tumor.

The rationale rests on why viruses thrive in cancer. A normal infected cell slows its machinery, signals for immune help, and can trigger self-destruction, taking the virus with it. A cancer cell can do none of this well; its hyperactive, unhinged growth disables those brakes, its ability to summon help is muted because the immune system is already trying to eliminate it, and its self-destruct switch is broken. Many tumors also build a chemical shield that hides them from immune cells.

The idea is old but the execution is hard. Doctors noted tumor shrinkage during influenza or measles in the early twentieth century, experimental inhibition by tickborne encephalitis strains in mice followed in 1951, and large clinical steps came with adenovirus H101 in China in 2004 and herpes-based T-VEC for melanoma in the United States in 2015. Still, virotherapy must orchestrate three complex actors — virus, cancer, and immunity — inside a person who must survive the battle, and cancers vary so much between people that a single agent rarely fits many.

In the lab, viruses are grown in cell cultures and roughly purified; the resulting liquid contains debris and is far from the purity required for human use. Halassy judged the risk acceptable for herself and picked as first agent the weakened measles strain used for more than four decades in childhood vaccines — not the wild virus that still killed about a hundred thousand people in 2024, but its tamed counterpart known to infect the cell type her tumor came from. The second agent was vesicular stomatitis virus, a distant, much milder relative of rabies that at worst causes brief flu-like symptoms.

Dosing proceeded every few days for weeks, starting with about six hundred thousand measles particles and totaling at least eighty million. Little changed after the first injection, the tumor then nearly doubled and looked more spiky and aggressive after the second, and thereafter began to shrink and soften. Throughout, oncologists at University Hospital Zagreb followed her closely, ready to switch to chemotherapy if needed.

Inside, the tumor became a battlefield. Viruses infected and killed defenseless cancer cells and multiplied, spilling dead-cell fragments and new virions into surrounding tissue and tearing the tumor's chemical shield. That flood of death signals jolted the immune system awake. Millions of immune cells poured into the mass — the reason for the explosive swelling — and a chaotic massacre followed, with viruses killing cancer, immune hunters consuming viruses, and cancer killers destroying malignant cells while the tumor tried to blunt immunity where it could.

Because immunity to measles rose quickly, Halassy switched to VSV after a few weeks; fever and chills appeared a day after the first VSV dose but remained her only notable side effects. After two months the tumor was about sixty-three percent smaller, softer, less dense, and had stopped invading muscle and skin. When surgeons removed it, half its mass consisted of lymphocytes still attacking cancer, a direct sign the immune response had arrived.

Surgery was followed by a year of trastuzumab, a standard drug for this breast cancer subtype, and Halassy has remained without recurrence for more than four years, approaching six years by the time the video was assembled. The experience redirected her laboratory toward virotherapy. Yet this remains a single, self-administered experiment without ethics-committee approval, under extraordinary personal expertise and monitoring; its publication was rejected more than a dozen times before Vaccines accepted the report.