Lung Cancer Can Remain Dormant for 20 Years: Treatment Challenges

Lung cancer can lie dormant for more than 20 years before turning deadly, which may explain why the disease kills >1.5 million people worldwide each year yet remains difficult to treat.

Two papers detailing the evolution of lung cancer reveal how after an initial disease-causing genetic fault, tumor cells quietly develop numerous mutations, making different parts of the same tumor genetically unique.

Once symptoms present and patients are diagnosed with cancer, their tumors will have developed down multiple evolutionary pathways, making it extremely difficult for any 1 targeted medicine to have an effect. The findings show the pressing need to detect lung cancer before it has shape-shifted into multiple malignant clones.

Lung cancer is the world's deadliest cancer, killing an estimated 4300 people each day, according to the World Health Organization. Approximately 85% of patients have non-small cell lung cancer (NSCLC), the type analyzed in the 2 recent studies.

In order to better understand the disease, 2 groups of British and American scientists examined genetic variability in different regions of lung tumors removed during surgery and worked out how genetic faults had developed over time.

They found an extremely long latency period between early mutations and clinical symptoms that finally appeared after new, additional faults triggered rapid disease growth.

In the case of some former smokers, the initial genetic faults that started their cancer dated back to the time they were smoking cigarettes 2 decades prior. But these faults became less important over time and more recent mutations were caused by a new process controlled by a protein called APOBEC.

There are also hopes for a new generation of immunotherapy drugs that boost the immune system's ability to detect and fight tumors, which could be particularly applicable to lung cancer. In addition to better treatment options, a critical challenge is to find improved ways to detect lung cancer before it develops the multiple genetic faults that eventually trigger rapid tumor growth and spread.

Currently, doctors use computerized tomography scans to detect lung cancer, but by the time a nodule is big enough to be spotted on a scan, it may contain a billion genetically diverse cancer cells.

Oncologists are hopeful for a new approach called liquid biopsy that may be able to detect signs of cancer much earlier from DNA circulating in the blood.

The current prognosis for NSCLC is grim, with most patients diagnosed when the disease has already spread and only around 15% of patients survive for at least 5 years after disease onset.—Kerri Fitzgerald

Source: Thomson Reuters. 2014; Scientists find lung cancer can lie hidden for 20 years.