Image source: Flickr user Alex Santos Silva.

You may not realize it, since most of the attention going to drugmakers recently has been focused on their drug pricing practices, but 2015 has been another successful year in terms of drug development.

This year we've witnessed the approval of two next-generation LDL-cholesterol-lowering injections (Repatha and Praluent), Darzalex for third-line and beyond multiple myeloma, Kanuma for lysosomal acid lipase deficiency, Genvoya for the treatment of HIV, and Ibrance for certain types of advanced breast cancer. This is literally just a snippet of the approvals that crossed the desk of the Food and Drug Administration in 2015.

But it's not just about the drug approvals we witnessed -- it's about the impact certain drugs and drug developers had on overall survival in 2015. Here are four drugs (two approved, and two still in development) that led to a doubling in overall survival based on clinical data released this year.

Atezolizumab -- Roche (OTC:RHHBY)
My personal selection for the most exciting clinical study of 2015 goes to Roche's atezolizumab, an anti-PDL1 immunotherapy that it's currently testing on a small army of solid tumors.

Image source: Roche.

The study of interest is the midstage POPLAR trial in advanced non-small cell lung cancer patients who've previously progressed on other treatments. Atezolizumab was targeted specifically at patients with the highest levels of PD-L1 expression, and the results demonstrated that it doubled the likelihood of survival in patients taking the drug relative to the placebo. Patients who express PD-L1 at a high or medium level also showed an improvement in overall survival as measured by the hazard ratio.

Cancer immunotherapies like atezolizumab work by turning off cancer's ability to go undetected by your immune system, thus giving your immune system a fighting chance to detect and destroy cancer cells. I'd expect atezolizumab to reach blockbuster status if it reaches pharmacy shelves.

Yervoy -- Bristol-Myers Squibb (NYSE:BMY)
Of currently approved products, perhaps the biggest upside surprise came from Bristol-Myers Squibb's Yervoy, a cancer immunotherapy that binds with CTLA-4 and inhibits CTLA-4's interaction with its ligands. Inhibition of CTLA-4 has been shown to increase T-cell response (T-cells are the detectors and destroyers of foreign cells within our immune system).

Image source: Bristol-Myers Squibb.

The study in question was a five-year survival rate analysis published in the Journal of Clinical Oncology. The trial looked at advanced melanoma patients who had taken the front-line combination of Yervoy and decarbazine and compared the five-year survival rate to patients taking a placebo and dacarbazine. Although initial survival data demonstrated only a 2.1-month median overall survival advantage for the Yervoy/dacarbazine combination, at the five-year mark 18.2% of the Yervoy-treated group were still alive compared to only 8.8% of the placebo-treated group. It's important to note that this improvement in survival is only experienced in about 10% more patients overall, but that's still a strong step in the right direction, and a big confidence boost for Yervoy's long-term potential.

VB-111 -- VBL Therapeutics
OK, so I'm cheating just a tiny bit on this one, but I promise it's still well worth it.

Image source: Bristol-Myers Squibb.

VBL Therapeutics and its experimental gene therapy VB-111 delivered a substantial improvement in median overall survival in continuous and intermittent doses for recurrent glioblastoma patients as compared to FDA-approved Avastin. Researchers at the Cancer Therapy and Research Center at the University of Texas Health Science Center at San Antonio presented results on their 62-patient midstage study in early October, demonstrating an approximate 15-month survival rate for VB-111 patients compared to just an eight-month survival rate for the Avastin arm -- a near doubling.

VB-111 is an intriguing drug candidate not only because of its angiogenic capacity to block new blood vessel growth to tumors and starve them of oxygen, but also because of the notion that VB-111 is only activated by a factor released by the tumor. It's a "smart" drug in every sense of the term, and it appears to have dramatically improved survival rates in patients with an aggressive cancer type who usually don't have very long to live. This is definitely a company worth keeping on your radar.

Aspirin -- Bayer (OTC:BAYR.Y)
Lastly, if you want a real curveball, scientists from Leiden University Medical Centre in the Netherlands analyzed data from 13,715 gastrointestinal cancer patients and made quite the shocking discovery when it came to patients who took aspirin. Yes, the type you can buy over the counter.

Image source: Flickr user Mike Mozart.

According to data presented by researchers at the European Cancer Congress, 30.5% of patients had used aspirin prior to being diagnosed with gastrointestinal cancer, 8.3% began taking aspirin following their diagnosis, and 61.1% of gastrointestinal cancer patients didn't use aspirin at all. What researchers found was that those who started taking aspirin after their diagnoses were twice as likely to be alive four years after their diagnosis compared to the patients who didn't take aspirin. Researchers also did their best to adjust for certain factors such as age, stage of cancer, the types of treatment offered, gender, and co-morbidities that may have altered the results.

How is aspirin fighting back against cancer? Researchers aren't entirely certain, but they postulate that the reduction in platelet count caused by aspirin makes cancer cells more visible to the immune system, thus reducing their ability to hide. Since platelets are necessary for the clotting process, cancer cells could essentially "hitch a ride" throughout the body and be masked by platelet activity. But regardless of the reason, aspirin-based compounds could offer new hope for improved overall survival in select cancer types. 

There were a lot of exciting, positive events in 2015, and I look forward to keeping that trend intact as we dive headfirst into 2016.

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.