Researchers say a programmed herpes virus can activate the immune system into attacking advanced stage liver tumors.

Liver tumors are tough to treat. But injecting these tumors with a herpes virus just might shift the body’s immune system into attack mode.

Cancerous tumors protect themselves by tricking the immune system into thinking they’re healthy, normal tissue. So, researchers are experimenting with using precise, image-guided injections of a genetically modified version of herpes.

The talimogene laherparepvec (T-VEC) virus is programmed to directly attack tumors as well as to change the protein structure on the surface of cancer cells. This allows white blood cells to flag them as foreign bodies for removal.

“We want to see if we can harness the power of the body’s own immune system to attack cancer wherever it appears,” Dr. Steven S. Raman, the study’s lead author and a professor of radiology, surgery, and urology at the David Geffen School of Medicine at the University of California at Los Angeles, told Healthline. “It’s basically waving a red flag at the immune system and saying, ‘Here I am.’”

The study, which hasn’t been published in a peer journal yet, was presented today at the Society of Interventional Radiology’s annual scientific meeting.

T-VEC was approved by the U.S. Food and Drug Administration (FDA) for treatment of melanoma in 2015.

Manufactured by pharmaceutical company Amgen, it’s never before been used to treat liver tumors.

“T-VEC still hasn’t taken off on melanoma,” Dr. Aaron Sasson, chief of surgical oncology at Stony Brook University Cancer Center in New York, told Healthline. “It’s more hit or miss and hasn’t produced the consistent results people were hoping for.”

Injecting substances into cancerous tumors to shrink or kill them isn’t a new technique. Alcohol injections have been used against liver tumors for decades, for example.

However, modern imaging equipment has made such procedures more precise and effective. The T-VEC experiment also adds advanced genetic engineering to the mix.

“It’s exciting that there might be another tool against tumors,” Dr. Adrian Legaspi, medical director of Tenet Florida Physician Services Center for Advanced Surgical Oncology, told Healthline. “If it’s more effective, or cheaper, or safer, we don’t know.”

A phase I clinical trial showed that T-VEC can be safely injected into the liver, according to the latest study’s authors.

The study involved 14 participants with metastatic liver cancer, including some who had cirrhosis.

Each was injected with escalating doses of T-VEC up to the effective dose used to treat melanoma. Dosage was calibrated to the size of each tumor.

“It seems like the dose tolerated well in melanoma patients can be tolerated well in liver patients,” said Raman.

Side effects were limited to known problems associated with T-VEC in patients with melanoma, such as temporary flu-like symptoms.

“This treatment needs to be done in a very controlled way so we don’t metaphorically light the immune system on fire and burn the whole house down,” Raman said.

Treating liver tumors can be difficult. The liver is complex, and patients are often in poor health heading into treatment.

Tumors, too, aren’t all created equal.

Sasson called the use of T-VEC to treat liver cancer a “novel concept,” but added: “I suspect there are going to be some tumors that are more immunoresponsive than others.”

Current options include surgery or freezing to destroy tumors. Other forms of injections, called ablation, are used, as well as embolization. That’s the use of tiny beads to block the blood supply feeding the tumor. Another option is radioembolization, which uses the bloodstream to carry radioactive material into the tumor in order to kill it.

“This minimally invasive treatment offers patients a novel way to directly and indirectly attack the cancer cells,” Raman said of T-VEC therapy, which he called “an advanced form of directed chemotherapy.”

Most liver cancers are metastatic, meaning they began in other parts of the body, often the colon, before moving to the body’s largest abdominal organ.

“Most cancers go to the liver at some point, especially end stage,” said Raman.

Primary liver cancer — those tumors that begin in the liver — are less common, but a “growing problem,” largely due to obesity, Raman noted.

Further study will be needed to determine T-VEC’s effectiveness in stimulating the immune system and shrinking or eliminating tumors.

If the therapy proves effective in treating liver tumors, there’s no reason to think it wouldn’t work on cancers in other parts of the body, Raman said.

“We can’t say that anyone has been cured or that there was a significant response, but we can see that it activated the immune system,” Raman said.

The first results of the study are expected to be published in an academic journal by the end of this year, but Raman cautioned that “this treatment will not be available for several years, except through clinical trials.”