Is now a good time to buy stocks? Given that we have yet to see the full economic impact of the COVID-19 pandemic -- and that equity markets may see even more turbulent days ahead -- some might choose to refrain from purchasing stocks altogether. However, long-term investors may want to take this opportunity to buy stocks at reasonably attractive valuations. After all, even after its recent rebounds, the S&P 500 is still down by 13.6% year to date, and many stocks now sport much lower price-to-earnings ratios than they did at the beginning of the year.

Even without the incentive of more attractive valuations, though, some stocks are worth serious consideration. Here are two stocks you should consider buying if you have an extra $1,000 laying around: CRISPR Therapeutics (CRSP -4.98%) and Exelixis (EXEL -0.68%).

A leader in gene editing 

CRISPR Therapeutics develops treatments that employ gene editing, a technology that replaces the defective genes responsible for causing certain illnesses with correct versions of the gene. The company currently has several exciting products in its pipeline including a trio of potential cancer treatments, CTX110, CTX120, and CTX130. But all three are still in early testing phases, and none will hit the market anytime soon if they earn approval at all.

Doctor's finger touching DNA strand.

Image Source: Getty Images.

CRISPR Therapeutics' most promising candidate is CTX001, a potential treatment for the blood disorders sickle cell disease (SCD) and transfusion-dependent beta thalassemia (TDT).

Last year, CRISPR Therapeutics announced positive results from a phase 1/2 clinical trial for CTX001. The trial involved two patients, one with SCD and one with TDT. Four months after being treated with CTX001, the patient with SCD did not experience any vaso-occlusive crises (a side-effect of SCD characterized by acute pain). Before the treatment, this patient experienced an average of seven vaso-occlusive crises per year (an average of about two crises in four months). The TDT patient was transfusion-independent nine months after the treatment. Before receiving the treatment, they required an average of 16.5 blood transfusions per year.

While these results are far from conclusive -- considering they involved only two patients -- they are still encouraging. Furthermore, thanks to its collaboration with Vertex Pharmaceuticals (VRTX -0.89%), CRISPR Therapeutics seems to have the funds necessary to support its operations for some time. In June, Vertex made an upfront payment of $175 million -- with the potential for additional milestone payments -- to enter into an exclusive licensing agreement with CRISPR Therapeutics. 

During the fourth quarter, CRISPR Therapeutics recorded revenues of $77 million, which compares favorably to the $115,000 in revenue it booked during Q4 2018. The company credited its partnership with Vertex for this significant increase. CRISPR Therapeutics also recorded a net income during the fourth quarter, which is rare for a clinical-stage biotech company. CRISPR Therapeutics' net income for the fourth quarter was $30.6 million. Lastly, the company had $943.8 million in cash and cash equivalents at the end of 2019, a 106.7% year over year increase. Thanks to its strong financial position, its partnership with Vertex Pharmaceuticals, and its exciting pipeline candidates, CRISPR Therapeutics looks like an exciting biotech stock to invest in.

A unique cancer medicine 

Exelixis is a biotech that focuses on developing cancer treatments. The company's crown jewel is Cabometyx, a tyrosine kinase inhibitor (TKI) that specifically targets cancer cells. Cabometyx treats several forms of cancer, including a type of liver cancer called hepatocellular carcinoma (HCC) and a form of kidney cancer called renal cell carcinoma (RCC). And while there are other treatments for both HCC and RCC, Cabometyx has one major thing going for it.

Namely, it is the first and only therapy to demonstrate significant improvement in three key efficacy parameters for RCC patients: overall survival, objective response rate (the percentage of patients whose cancer is reduced after treatment), and progression-free survival (the amount of time during and after treatment the patient lives with cancer without experiencing worsening symptoms).

According to Exelixis Senior Vice President P.J. Haley, Cabometyx is the most-prescribed TKI for RCC and HCC patients. The therapy continues to post strong sales growth, too. For fiscal 2019, Exelixis reported net product revenue of $760 million, up from $619.3 million in fiscal 2018. Exelixis attributed that growth to the continued success of Cabometyx.

Furthermore, there are good reasons to think sales of the cancer treatment will continue to increase. Health Canada approved Cabometyx late last year for the treatment of advanced RCC, as well as for patients with previously treated HCC. On March 25, Exelixis announced that Takeda Pharmaceuticals (TAK -0.81%) -- which holds the rights to Cabometyx in Japan -- received approval from the Japanese Ministry of Health for its use as a treatment for RCC. Exelixis will receive royalties from Takeda for the sale of Cabometyx in Japan. 

Thanks to the continued success of its crown jewel therapy, Exelixis looks like a biotech stock worth adding to your portfolio.