Image source: National Cancer Institute.

Cancer is arguably the most terrifying diagnosis a patient can get. The reason cancer can be so scary, aside from the fact that it was the second-leading cause of death in the United States as of 2013, is that there are very few functional cures. Researchers are still working to unlock the secrets behind cancer, such as why one person gets it and another person doesn't despite having similar risk factors.

A ray of sunshine in a gloomy forecast
But, there's another side to the tale of fighting cancer -- one of hope. Based on the American Cancer Society's "Cancer Facts and Figures 2015" report, we're witnessing slow but steady progress in terms of improving quality of life and length of life for most cancer types. For instance, between 1975 and 1977, some of the most commonly diagnosed cancers -- breast, prostate, and colon cancer -- had five-year survival rates of 75%, 68%, and 51%, respectively. As of data between 2004 and 2010, breast, prostate, and colon cancer five-year survival rates are now 91%, greater than 99%, and 65%.

The big key in treating cancer has always been early detection. Catching cancer in a localized state before it's had a chance to spread often means a much better chance at effectively fighting, and possibly even curing, the cancer in question. For instance, a lung cancer diagnosis is often thought of as a death sentence, but that's not necessarily the case anymore. Localized lung cancer results in a five-year survival rate of 54%. It's when the original tumor spreads to distant parts of the body (known as metastasis) that five-year survival rates for lung cancer drop to just 4%. 

Former President Jimmy Carter. Image source: Jimmy Carter.

Jimmy Carter tackles cancer and wins
One high-profile cancer case that captivated the nation this summer was the announcement that former U.S. President Jimmy Carter had cancer. Not only did Carter, 91, have cancer, but he had metastatic melanoma, an aggressive form of skin cancer that had spread to his liver and created four 2 mm spots on his brain. ACS data shows us that localized melanoma results in a 98% five-year survival rate. However, once it metastasizes to other parts of the body, five-year survival rates drop to just 16%. The ACS estimated earlier this year that 73,870 new cases of melanoma would be diagnosed in 2015.

Put plainly, Carter didn't have the best prognosis even though he remained in good spirits. Both of Carter's parents, his only two sisters, and his lone brother all died from cancer. From the perspective of genetics, Carter appeared to be at a high risk of developing cancer from the get-go.

Then a miracle happened -- or should I say a miracle drug. Just this past week Carter confirmed, along with tweets from two of his grandsons, that he is now cancer free. Not only is Carter free of the four spots detected on his brain, but the original tumors are gone as well.

Meet the miracle drug behind Carter's cancer cure
The miracle drug that led to Carter's cure is none other than hyped cancer immunotherapy drug Keytruda from Merck (NYSE:MRK).

Image source: Merck.

Immunotherapies are a new class of cancer fighting drugs that work by enhancing the ability of your immune system to locate and destroy cancer cells. Keytruda itself is a checkpoint inhibitor that aims to remove the immunosuppressant quality of cancer cells which allows them to go undetected by the immune system. Once exposed, your immune system can kick into high gear and fight back against foreign cancer cells.

To date, Merck's Keytruda and Bristol-Myers Squibb's (NYSE:BMY) Opdivo are the best known checkpoint inhibitors. They are both approved to treat a type of metastatic melanoma, and each recently gained approval to treat select advanced non-small cell lung cancer patients. For Carter, Keytruda demonstrated its incredible efficacy by ridding the former president of what had become a globalized cancer within his body. However, it could be select patients with advanced NSCLC who derive even more benefit.

Speaking on a generalized basis, patients with advanced NSCLC typically have a response rate of around 25% when trying a second-line therapy. Merck's Keytruda and Bristol-Myers Squibb's Opdivo, which have both demonstrated an affinity for efficacy in patients whose tumors express high levels of PD-L1, produced response rates of around 60% in high PD-L1-expressing patients during clinical trials.

We've really just touched the tip of the iceberg in terms of what could be possible for cancer immunotherapies, as Keytruda and Opdivo are looking to expand to multiple solid tumor, and perhaps even blood cancer, indications in the coming years.

Plenty more where this came from
Amazingly, there could be many more immunotherapy drugs on the way for cancer patients before the decade is over.

Image source: Merck KGaA.

Pfizer (NYSE:PFE) and Merck KGaA (NASDAQOTH: MKGAY) are working on an experimental immunotherapy known as avelumab which has demonstrated similar promise to Keytruda and Opdivo. Rather than tackle metastatic melanoma, which most drug developers have used as the stepping stone approval to other indications, Pfizer and Merck KGaA are working on a late-stage study (JAVELIN LUNG 200) for advanced NSCLC, and have a number of early stage solid tumor trials ongoing, including bladder cancer, gastric cancer, head and neck cancer, mesothelioma, renal cancer, and ovarian cancer.

But I want to be clear that immunotherapy development isn't limited just to big-name pharmaceutical companies. Inovio Pharmaceuticals has roughly a half-dozen cancer immunotherapies in development, Peregrine Pharmaceuticals is working on an immunotherapy drug of its own for second-line NSCLC, and Galena Biopharma has an intriguing adjuvant vaccine known as NeuVax in late-stage clinical studies that's attempting to stop the recurrence of breast cancer in the post-treatment setting.

Cancer is a scary diagnosis, but these are exciting times when it comes to advancements in cancer meds. Although we're not talking about "flip-the-switch" cures, we are, undoubtedly, making serious strides in the right direction toward better quality of life, and potentially longer lives, for today's cancer patients.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.