Growth stocks are usually known to capitalize off short-term consumer trends. However, the best growth companies are the ones that set aside a portion of their revenues each quarter and reinvest back into innovation.

That kind of discipline is extremely hard to come by. Luckily, Roblox (NYSE:RBLX) and Novocure (NASDAQ:NVCR) are two fantastic companies that happen to possess it. Here's how the online game platform and the cancer-fighting biotech can add muscle to your portfolio. 

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1. Roblox

Roblox is a do-it-yourself video game publishing platform with over 40 million games enjoyed by 42.1 million active users each day. Players are able to socialize with one another from around the world while having access to games on nearly all consoles, as well as spending its digital currency Robux to unlock better in-game experiences. 

During the first quarter of 2021, Roblox's revenue and free cash flow increased by 140% and 311% year over year, respectively, to $387 million and $421.1 million. What's more, these trends are reaching well into the second quarter. In April, the company's sales increased by 138% to $144 million. 

A big reason behind Roblox's success is its commitment to innovation and its clients. The firm pays out as much as 31% of its sales to game developers. In addition, another 24% of revenue went into developing the platform infrastructure, as well as moderation to maintain trust and safety in the community. 

Right now, Roblox stock may seem a little expensive at 21.3 times estimated fiscal 2021 sales. However, keep in mind that the company is growing its sales by upwards of triple-digit percentages, so it is well worth the premium. Due to its high-value proposition, scalable business model, and consistent reinvestment back into its platform, Roblox is one of the top tech stocks to buy now. 

2. Novocure

Novocure is at the forefront of using innovative technology to combat cancer. Its flagship product, Optune, is a wearable and portable device that delivers alternating electric fields (Tumor Treating Fields, or TTFs) to disrupt the ability of cancer cells to multiply. Researchers carefully tailored the frequency so that it would only destroy malignant cells and not healthy ones.

The device is currently indicated for the treatment of glioblastoma (a deadly form of brain cancer) and mesothelioma. In Q1 2021, Novocure's revenue grew by 32% annually to $134.7 million. Simultaneously, the company's operating income less noncash items (EBITDA) increased by 40% to $21.415 million. 

There are now 3,454 active patients receiving care via Optune, and that number is about to rise sharply. On May 18, Novocure announced that the U.S. Food and Drug Administration agreed to reduce the number of patients enrolled in a phase 3 trial to test the efficacy of TTFs in targeting advanced stage non-small cell lung cancer (NSCLC). According to an independent committee monitoring the study: "... it is likely unnecessary and possibly unethical for patients randomized to the control arm of the trial to continue accrual according to the original protocol."

It can only be considered unethical for patients to receive the control treatment when the experimental therapy has a huge clinical benefit. Hence, the approval of TTFs for NSCLC is almost guaranteed at this point, especially considering that there was no evidence of toxicity in the study. Keep in mind that this is a market forecasted to reach $48 billion by 2026.

Aside from that, Novocure is also investigating TTFs for targeting brain metastasis, pancreatic cancer, ovarian cancer, liver cancer, and gastric cancer. Like Roblox, the company dedicates much of its revenue (close to 34%) to research and development so that its growth is sustainable for the long term. Overall, it is a well-rounded healthcare stock to consider for one's portfolio. 

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.