Bolstered by new data presented at a key medical conference, Aptose Biosciences’s (NASDAQ:APTO) stock bolted skyward in December, more than doubling in price. Savvy investors looking for exposure to the high-risk, high-reward biotech sector need to look no further.The company’s lead drug, CG-806, inhibits a cancer target called Bruton’s tyrosine kinase (BTK). BTK emerged as a promising target and inhibitors rapidly advanced through the clinic as treatments for chronic lymphocytic leukemia (CLL), one of the most common forms of leukemia, and other blood malignancies. FLT3 mutations occur in roughly 30% of acute myelogenous leukemia (AML) patients, according to a 2019 publication in the scientific journal Leukemia.These two blood cancers present a lucrative opportunity if CG-806 works. The National Cancer Institute (NCI) states that more than 20,000 people in the U.S. were diagnosed with CLL in 2019 and more than 178,000 in the U.S. lived with the cancer in 2016. More than 61,000 people in the U.S. live with AML and nearly 11,000 died of the cancer last year, according to the NCI.Aptose claims CG-806’s ability to inhibit all forms of BTK and FLT3, including those that have mutations, makes it unique. Furthermore, it binds to a different location on the BTK enzyme than other inhibitors, including those that have already been approved. For these reasons, Aptose believes patients who stopped responding to other BTK inhibitors could respond to CG-806 treatment.Imbruvica leads the BTK inhibitor pack. Pharmacyclics initially developed the drug until Johnson & Johnson (NYSE:JNJ) entered into a 50/50 co-development partnership in December 2011. Pharmacyclics stock jumped from the mid-teens to around $30 per share on the news. Fast forward to spring 2015, when AbbVie (NYSE:ABBV) bought Pharmacyclics for $21 billion, or $261.25 per share. Keep in mind, that’s for Pharmacyclics’ half of Imbruvica. In 2019, Imbruvica generated $4.67 billion in sales for AbbVie and $3.41 billion in sales for Johnson & Johnson.Seeking to get a piece of the action, AstraZeneca (NYSE:AZN) bought privately held Acerta Pharma in December 2015 for up to $7 billion for its BTK inhibitor. In November 2019, the FDA approved the drug called Calquence for the treatment of CLL, following a 2017 approval as a treatment for mantle cell lymphoma, an aggressive form of non-Hodgkin’s lymphoma with a poor prognosis.Brukinsa, a BTK inhibitor approved for patients with mantle cell lymphoma who had at least one prior treatment, gained FDA approval in November 2019, marking the first FDA approval for the China-based drug developer BeiGene (NASDAQ:BGNE).What’s the takeaway? First, BTK inhibitors are a proven class of drug. Second, big pharma has a history of paying considerable sums of money for successful BTK inhibitors. If Aptose proves CG-806 benefits CLL patients that failed prior BTK therapy, then a big suitor could write a large check for the company rewarding shareholders.As with BTK, precedent exists for Aptose pursuing FLT3. Novartis (NYSE:NVS) markets the drug Rydapt, and Japanese company Astellas Pharma sells Xospata as treatments for AML patients with FLT3 mutations. Aptose touts CG-806’s superior potency over other FLT3 inhibitors based on testing in more than 200 AML samples. Aptose announced in January that the phase 1 trial is now enrolling the fourth cohort of patients.For a bit of historical perspective, AML had few new treatments for decades until the relatively recent approvals for Novartis, Astellas, and Jazz Pharmaceuticals (NASDAQ:JAZZ). Jazz gained approval in 2017 for Vyxeos, a fixed combination of two older chemotherapy agents that provided the backbone for treatment of AML.Vyxeos was originally developed by Celator Pharmaceuticals, a small biotech that struggled to gain attention for its combo product. However, when its phase 3 trial demonstrated a benefit in overall survival, the stock shot through the roof, from under $2 to the mid-teens. Shortly thereafter, Jazz bought the company for $30.25 per share, or $1.5 billion. Some fortunate investors experienced a 15-fold return within months.Why do I highlight these deals from the past? In many cases, small companies like Aptose never commercialize a drug. Much like the farm system in baseball, small biotechs develop drugs that big pharma and biotech companies ultimately sell. Either the drug is licensed to a bigger company with commercial capabilities or the smaller company is outright acquired. In my opinion, Aptose will not commercialize this drug but rather do one of these types of deals. The big unknown for investors is when will a deal occur, if at all.Let’s just do a back of the envelope analysis on CG-806’s potential. Using the NCI’s prevalence numbers, there are approximately 239,000 eligible patients (178,000 CLL and 61,000 AML). Let’s assume half are diagnosed and receiving treatment. That gives us 119,500 treatable patients. If we assume 15% market penetration and a price of $120,000 annually ($10,000 per month), the annual revenue exceeds $2.15 billion. Divide that by the 76.1 million shares outstanding results in revenue over $28 per share, and that’s only for a single year. Simply put, the $7.85 stock price may look cheap in hindsight if the drug performs.Biotech stocks like Aptose, are high-risk, high-reward investments. Speculative investors may wish to add some to their portfolios for potentially huge upside. As demonstrated by both the Pharmacyclics and Celator acquisitions, 10- to 20-time returns can happen in certain situations. Aptose, if successful, will likely be an acquisition target for a hungry pharma looking to replenish its pipeline.