Lung cancer can remain hidden for up to 20 years before symptoms begin to display themselves, according to a new study.

Smoking or other causes can trigger a genetic fault in genes within lungs. Tumor cells then quickly multiply and diversify. Growths develop, containing differing genetic codes within their masses, making treatment more difficult. Most patients are not diagnosed with the disease until the tumor has already developed a wide range of genetic bases. Targeted medicines, aimed at a single characteristic in a cell, may be effective against some portions of a tumor, while remaining inert against other portions of a growth.

Lung cancer kills around 4,300 patients each day, more than 1.5 million people each year, across the globe, making it the world's deadliest cancer. Just 15 percent of patients survive five years past initial diagnosis.

Medical researchers studied samples of lung cancer tumors taken from patients at various stages of lung cancer, in an effort to understand how genetic faults developed over the course of the disease. They found that these cancer cells underwent a long latency period between the development of genetic mutations and a phase of rapid growth that usually triggered diagnosis. This rapid growth is set off when additional genetic faults form, resulting in the creation of additional tumor cells.

"What we've not been able to understand before is why this is really the emperor of all cancers and one of the hardest diseases to treat. Previously, we didn't know how heterogeneous these early-stage lung cancers were," Charles Swanton of the London Research Institute, and co-author of one of a pair of articles prepared on the study, said.

This discovery could help explain why the disease is so difficult to treat, and so pervasive among patients.

"On average, 76 percent of all mutations and 20 out of 21 known cancer gene mutations were identified in all regions of individual tumors," Jianjun Zhang of the University of Texas and others, wrote in an article detailing the study.

This genetic diversity may be the "Achilles heel" for the tumor, as a new generation of drugs are being developed, able to boost the human immune system, assisting it in fighting tumors. Every new form of the cancer cell provides a new opportunity for the body to recognize and fight the disease.

Doctors usually turn to computerized tomography (CT) in order to diagnose lung cancer. However, the technology is not able to detect a tumor until around one billion tumor cells collect in a growth. This new research shows these cells could already show a wide genetic variety.

Lung cancer evolution, and the role played by genetic diversity in development of the disease, was detailed in the journal Science.

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