Study finds inverse link between cancer, Alzheimer's

Karen Weintraub | Special for USA TODAY

In a small bit of good news for people with terrible diagnoses, having cancer appears to protect against getting Alzheimer's disease -- and vice versa.

What began as a hunch by a handful of researchers is confirmed in a study published today in the journal Neurology. People diagnosed with Alzheimer's were found to have a 43% lower risk of developing cancer than those without the disease, and people with cancer ran a 35% lower chance of developing Alzheimer's, according to the study of 25,000 residents of the Italian city of Milan.

This inverse relationship between cancer and Alzheimer's will be one of the key topics discussed at the Alzheimer's Association International Conference in Boston, beginning this weekend. The conference is expected to include more than 4,500 researchers from 66 countries, and cover subjects such as Alzheimer's risk factors, early detection, imaging and treatment.

Alzheimer's is projected to triple over the next generation and become a huge social and financial burden. People with Alzheimer's suffer loss of memory, thinking and language skills as well as behavioral changes that can make them extremely challenging to care for. Current treatments do not address underlying symptoms or stop the progression of the fatal disease.

"Alzheimer's is a disease that is going to dwarf every other disease, in terms of cost, in terms of effect on people's lives, and we're not as far ahead as we should be," says Jane A. Driver, an epidemiologist, oncologist and geriatrician at the VA Boston Healthcare System and Brigham and Women's Hospital.

No one knows for certain why Alzheimer's and cancer are inversely related.

Massimo Musicco, the lead author of the new paper, says he thinks that the two are simply different facets of aging. If you have one set of genes, you are likely to take one disease pathway as you age; another set of genes will direct you along a different route, he says.

Driver, who was not involved in the new study but has led similar research, says she thinks the two conditions are likely caused by opposite genetic activity. Cancer is essentially a disease where cells reproduce too much and refuse to die; in Alzheimer's and related diseases like Parkinson's, brain cells – which can't reproduce – die off too quickly. She is currently developing potential drug candidates that increase or reduce activity of a gene, PIN1, which seems to be involved in both diseases.

The interrelationship also raises questions about drug development. If someone found a drug to effectively treat Alzheimer's, might it cause cancer?

"That is something we have to think about," Driver says.

Not all cancers seem to offer the same protection against Alzheimer's. Prostate cancer isn't protective, according to the new study and other research, though scientists aren't sure why.

The new study answers critics who had thought the inverse relationship could be explained simply: Someone with cancer or Alzheimer's might not live long enough to get the other. But the new research found that is not the case. The cancer diagnosis rate was lower for people who were later diagnosed with Alzheimer's and vice versa, Musicco says.

Catherine Roe, of the Washington University School of Medicine, says fellow scientists laughed at her in 2005 when her own research first suggested a link between Alzheimer's and cancer. Roe said she was able to follow up that study when she met another researcher at the Alzheimer's Association International Conference, who became her collaborator.

Roe says she's excited that the new study has confirmed her earlier findings and that more scientists will now take the connection seriously.

"It could open avenues of investigation that people haven't even thought of yet," she says. "They've been looking at the usual suspects for so long."