• The Food and Drug Administration on Thursday approved Amgen's treatment for patients with the most deadly form of lung cancer. 
• The agency cleared the drug, called Imdelltra, as a second or later-line treatment for adults with advanced small-cell lung cancer.
• In clinical trials, Amgen's drug has been shown to reduce tumor growth and help people with small-cell lung cancer live longer. 

The Food and Drug Administration on Thursday approved Amgen's therapy for patients with the most deadly form of lung cancer. 

The agency cleared the drug, which will be marketed under the name Imdelltra, as a second or later line of treatment for people with advanced small-cell lung cancer. That means patients can take the drug if their cancer progresses while on or after trying one other form of treatment, which is typically a type of chemotherapy. Amgen's drug is also known by its generic name tarlatamab.

In clinical trials, Amgen's drug has been shown to reduce tumor growth and help people with small-cell lung cancer live significantly longer.

Of the more than 2.2 million patients who are diagnosed with lung cancer worldwide each year, small-cell lung cancer comprises 15%, or 330,000, of those cases, Amgen said. Around 80% to 85% of people with small-cell lung cancer are diagnosed with an advanced stage of the disease, according to a study published in the Journal of Cancer.

There are around 35,000 patients with small-cell lung cancer in the U.S., Dr. Jay Bradner, Amgen's chief scientific officer, told CNBC. 

Small-cell lung cancer usually starts in the airways of the lung and grows rapidly, creating large tumors and spreading throughout the body. Symptoms include bloody phlegm, cough, chest pain and shortness of breath.

Only 3% of patients with small-cell lung cancer that has spread to other parts of the body live past 5 years, according to the American Cancer Society. That five-year survival rate accounts for 7% among all patients with the condition, regardless of whether the cancer spreads. Bradner said patients with small-cell lung cancer typically have four to five months to live.

Lynne Bell, a small-cell lung cancer patient from Atlanta, Georgia, is an exception. She says she was "horrified" and "in a dark place" after she was diagnosed with an advanced stage of the condition in 2021.

But she started taking Amgen's Imdelltra in an ongoing clinical trial in September after other treatments, including chemotherapy, stopped working. Since then, Bell said her tumors have shrunk significantly and cancer scans "look great." She said she specifically noticed her pain go away after taking a second dose of Amgen's drug.

When asked how long she would continue Imdelltra, Bell said, "If this medication is working and I'm not having any side effects, I'm good to go. I'm in it to win it."

Maida Mangiameli, a small-cell lung cancer advocate and patient mentor from Naperville, Illinois, is also a survivor of the devastating disease. She was diagnosed with an advanced stage of the condition in 2018 but was deemed in remission this year, meaning the treatment she received has reduced the signs and symptoms of the cancer. 

Mangiameli has been in remission for five years. Her treatments included chemotherapy and 28 days of radiation therapy. She told CNBC that Amgen's Imdelltra may "not be something for me, but it might be down the road." 

Mangiameli added that she's excited to know that there will be another therapy option for other patients suffering from small-cell lung cancer. She said the development of new treatments for the disease has been "on the back burner" for several years. 

Amgen's Bradner also said treatment options "are pretty meager." 

"It's just one of the most dreadful cancers and so we needed a new solution," he said. 

Amgen's drug is called a bispecific T-cell engager, which is designed to redirect the immune system's T-cells to recognize and kill cancer cells. 

The approval is based on results from a phase two trial that followed more than 200 patients with small-cell lung cancer. Cancer tumors shrank in 40% of people who were given a 10-milligram dose of Imdelltra every 2 weeks.

Notably, the median time that people lived after starting 10-milligram doses of Amgen's drug was 14.3 months. That compares with around six to 12 months with current treatments, according to the National Cancer Institute. 

"These patients who would normally only have four to five months enjoy almost another full year of life," Bradner told CNBC. 

That time can make a huge difference for patients. 

For Mangiameli, receiving treatment for small-cell lung cancer gave her years to get closer to her grandchild, who was born not long before she was diagnosed with the disease. 

"I had the impetus, the drive to make sure I survived. … I just had my first grandchild, I have to live long enough for us to become pals," Mangiameli said. 

Meanwhile, Bell said taking Imdelltra gave her the time to travel; she went on a trip with her daughter to San Diego.

"I'm trying to go as many places that I can get to," Bell told CNBC.

Amgen is continuing to study Imdelltra in several trials, including some that will test the drug as an earlier line of treatment for small-cell lung cancer. 

That includes a late-stage trial comparing Imdelltra with chemotherapy as a second-line treatment for the disease. Amgen also plans to start another phase three study on the drug as a first-line treatment for patients at an advanced stage of small-cell lung cancer. 

"What makes us hopeful is, as you develop cancer medicines, that if they work in later stages of the disease, they can work even better when you move them" to first-line treatment, Bradner said.