Targeted Cancer Therapy Kills Prostate Tumor Cells

Prostate cancer kills more people than breast cancer in the UK, yet it's been relatively neglected compared to diseases that affect parts of the body people prefer talking about. Now, however, the first trial of a newish form of radiation therapy has produced excellent results, with some cancers almost disappearing and many patients reporting less pain and improved quality of life.

Radiation is a standard tool in cancer treatment, used to kill tumor cells. However, when administered externally it also ends up damaging many previously healthy cells, with disastrous consequences. One solution is to make radioactive elements payload aboard molecules that home in on the tumor. Yet that becomes more challenging after the cancer has metastasized, spreading throughout the body.

Recently, however, an experimental therapy has been used that relies on molecules that can track down prostate cancer cells wherever they have spread.

The technique relies on the fact that prostate cancer cells, irrespective of location, produce receptors known as prostate-specific membrane antigens (PSMA) on their outer membranes. Certain molecules are able to find these receptors anywhere in the body and bind to it, and radioactive isotopes can be attached to these molecules and carried to the cancer cells.

The therapy is done in two stages. The first uses gallium-68 or fluorine-18, whose radioactivity is not strong enough to kill the cancer cells, but can be detected on PET scanners, producing an exceptionally detailed 3D map of the locations in the body the cancer has reached. This provides guidance as to the general areas to which therapy needs to be targeted.

Once this has been done, a new round of PSMA seekers are released, this time with lutetium-177 on board. Lu-177 is used because it produces high doses of beta radiation that kill nearby cells but do not spread far through the body. The technique, known as LuPSMA, has been used for men dying of cancer for several years, but there has been limited solid evidence for how well it works. For patients where all other treatments have failed, even the possibility of success can be enough to justify trying, but we need more evidence before applying it more broadly.

A paper in Lancet Oncology reports that among 30 participants for whom chemotherapy had failed, all but one showed measurable prostate specific antigen reductions when given LuPSMA, more than halving in 17 cases, and in one case disappearing entirely. Eleven of the 30 described a major reduction in disease, and most of the tumors that could be measured shrank. The results beat those from a previous study using the same technique but a different carrier molecule, and are encouraging enough that a larger trial has begun. 

[H/T: Australian Financial Review]

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