The experimental drug, Hamlet (Human Alpha-lactalbumin Made Lethal to Tumour cells), kills tumour cells seemingly without harming healthy cells.

Its potential was discovered by accident in 1995 by a research group at Lund University, Sweden, led by Professor Catharina Svanborg.

For the past 30 years the team has been developing and trialling Hamlet, a man-made version of a molecule found in breast milk, on a range of cancers in animals and humans.

A previous trial involving nine bladder cancer patients found that eight of them started passing tumour cells in their urine just two hours after being administered Hamlet, and that their tumour reduced in size or changed character. Adjacent healthy tissues showed no sign of toxicity.

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The current clinical trial, which is the largest to date, is taking place in Prague, in the Czech Republic, with a placebo-controlled group of bladder-cancer patients.

The drug is administered to patients via a catheter into the bladder and each patient will receive six doses over a one-month period before undergoing surgery.

Dr Matthew Lam, science communications manager at Worldwide Cancer Research, a UK-based charity that funds cancer research around the world, said: “This small, early-stage clinical trial is taking scientific knowledge gained through laboratory experiments into the clinic to test the treatment’s safety and efficacy.

“It will be a while until we know if the treatment is safe to progress into larger trials, and it will be years before we know if the treatment is more effective than the currently available treatment options … We look forward to hearing about future progress on this new way to treat cancer.”

Svanborg says Hamlet is unique in its ability to target specific tumours with apparently little or no side effects, unlike chemotherapy and radiotherapy – which destroy some healthy cells, causing side effects such as nerve damage, loss of hair and nausea.

“We believe the treatment points to new ways of reaching a balance between therapeutic efficacy and side effects,” Svanborg says, adding that the results will become available during the summer.

“The final results include a range of very exciting, molecular technologies and tissue analyses that will provide more precise tools to define the drug effect in each patient. A positive outcome of the bladder cancer study would help reinforce the potential of this new type of cancer therapy.”

Following the initial treatment stage, the 40 patients taking part in the clinical trial will be monitored for two years to enable researchers to analyse the long-term effect of the drug post-treatment.

Svanborg says her team is also developing solutions for other cancers, including brain tumours and colon cancer, which are hard to cure with current therapies.

They are also looking for partners to promote the development and distribution of the drug within specific cancer markets.

Their ultimate goal is for Hamlet to be used as a preventive measure worldwide.

“If efficacy can be combined with a lack of toxicity, it is possible that this treatment can be used both as prevention and therapy. The vision would be to make it available worldwide, to patients who are susceptible to certain cancers, or who suffer from tumours that can be reached and treated with this substance,” she says.

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Hamlet has been found to kill more than 40 types of cancer cells in laboratories to date and Professor Svanborg hopes that the current trial will demonstrate its effectiveness on humans.

Lam said: “It’s great to see new research ideas making progress towards potential new treatments for cancer, but this announcement is just one small step forward in a long research journey.”

The prospect of a cancer treatment replicated from human breast milk was the last thing Svanborg expected when she made the discovery with postgraduate student Anders Hakansson more than 30 years ago.

The original research involved experimenting with breast milk to understand how it was able to fight off germs.

A common scientific practice is to use human cancer cells in these tests because they behave similarly to other human cells and live indefinitely in laboratory dishes.

The researchers were surprised to discover that the cancer cells were disappearing, and on closer inspection, the professor realised the breast milk was causing them to “commit suicide”.

“Looking down the microscope at the dying tumour cells, we were quite excited, especially when the experiment was repeated and showed the same effect twice. We had used non-cancerous cells for a long time in similar experiments and they had not died,” Svanborg explains.

Further experiments confirmed that when human milk binds to a fatty acid it creates a unique tumour-killing protein-lipid complex that has the ability to destroy cancer cells. Svanborg found it rapidly shrunk the most aggressive type of invasive brain tumour, as well as bladder cancer and colon cancer tumours.

For the past three decades, Svanborg and her team of around a dozen scientists have been building up conclusive scientific data about the effectiveness of human milk protein in killing cancer cells.

Tests on mice showed Hamlet limited the development of brain tumours and bladder cancer. It also prevented the development of colon cancer in baby mice, when given in their drinking water, suggesting that it might also be used to prevent tumours developing in people whose genetic history makes them susceptible to cancer.

The work has been published in international journals including The New England Journal of Medicine, The International Journal of Cancer, Oncogene, Experimental Cell Research and Molecular Microbiology.

Svanborg says: “We have lived with this project for many years and wish to see it come full circle to reach the patients. To us, the molecule and its effects are the centre of attention and we are the facilitators; [it’s] a nice role to have.”