When we consider the stock market, we have a tendency to put ourselves in the shoes of investors decades ago, imagining we would have bought shares of companies that have since proven successful and and held on for the riches to come. Apple is a great example of this thinking. Its current market capitalization of nearly $2 trillion is solid proof that at the turn of the century, it was a great stock to buy.

But where are the great growth stocks of today? The ones we will one day look back on with admiration, the ones we should buy now and hold for the long term? Here are two growth stocks to buy and hold today -- or one day wish you had.

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1. DexCom

DexCom (NASDAQ:DXCM) makes continuous glucose monitors (CGMs) that help diabetes patients to better manage their condition. The discreet monitors provide a reading every five minutes to a receiver or smart device, allowing patients to adjust their behavior in real time. Diabetes is astoundingly prevalent throughout the world and especially in the U.S., with approximately 10.5% of Americans having the disease. The epidemic has gotten worse over time, with the median rate of diabetes per county in America at 13% in 2016, up from 7.8% in 2004. DexCom has led the way in technological advancements, from its original device -- which created the CGM market -- to the soon-to-be-released DexCom G7, a collaboration with Alphabet's (NASDAQ:GOOG)(NASDAQ:GOOGL) Verily.

The revolution in diabetes management has produced fantastic growth. Since 2010, the company has expanded its annual sales from $49 million to $1.8 billion -- that's an annual growth rate of 50%. During that stretch, the company's gross margin -- sales revenue minus expenses directly related to building the product -- has increased to 65% from 38%, and it recently reported a 61% jump in net income for the third quarter versus last year. And DexCom has plenty of growth opportunities left; management estimates that just 40% of the 1.25 million U.S. type 1 diabetes patients are using glucose monitors, and only 15% to 20% of the more than 30 million type 2 diabetes patients are using them.

The company does face competition, particularly from Abbott (NYSE:ABT), but it has maintained its technological advantage over the years. The partnership with Verily may one day yield an adhesive-bandage-style CGM that would transform life for diabetes patients around the world. When you consider the more than 84 million Americans with pre-diabetes in addition to the existing market, it's clear that DexCom has a good chance for impressive growth.

2. Exact Sciences

Exact Sciences (NASDAQ:EXAS) is a cancer diagnostics company that revolutionized testing for colon cancer with its Cologuard test, a one-of-a-kind procedure that looks for indicators of cancerous DNA in stool as an early screening for the deadly disease. The test is 97% accurate and is covered by all major insurance companies. After the U.S. Food and Drug Administration approved the product in 2014, sales exploded; from $2 million that year, they've hit more than $1.3 billion over the past 12 months. Despite the growth, the company does not yet turn a profit.

Management thinks colorectal cancer is only the beginning, believing its platform will support screening for many different kinds of cancers -- the company lists 12 in its presentation on the pipeline. In addition to accuracy in identifying multiple types of cancer, Exact Sciences's precision oncology unit offers tests that can predict the benefit of chemotherapy for individual breast cancer patients, predict the recurrence of colon and breast cancers, and identify prostate cancer patients who will not benefit from a common type of therapy. 

Although shutdowns slowed traditional testing volume this year, COVID-19 has also brought opportunities. The company reported $102 million in COVID-19 testing during the third quarter, triple what it saw in the second quarter. Further, DexCom received approval to test samples that are taken at home (though they still need to be ordered by a telehealth provider and processed in a lab). The at-home collection kits will be available this month.

Management thinks the largest market for these kits will be employers who want to test staff members before bringing them back to work. The service will include dashboards showing aggregated results and information about who is complying with the tests. This is only the most recent innovative solution from Exact Sciences beyond the stool test it is known for. With a dominant position in early screening for one type of cancer and a platform capable of testing for many others, Exact Sciences could one day be the gold standard for cancer testing. If management gets anywhere close to achieving its vision, growth investors will be profiting for years to come.

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.