It's not every day that shares in top companies can be bought at a reasonable valuation, so investors ought to pay attention when it happens. For instance, these three Motley Fool contributors believe Gilead Sciences (NASDAQ:GILD), Magellan Health (NASDAQ:MGLN), and Celgene Corp (NASDAQ:CELG) shares represent a unique opportunity to buy leading healthcare companies on sale. Are these stocks a good fit for your portfolio?

Shifting gears

Keith Speights (Gilead Sciences): Gilead Sciences CEO John Milligan is stepping down at the end of 2018. So is current board chairman and former longtime CEO John Martin. Other key executives have also left the company. The reality is that Gilead is shifting gears -- and that's a good thing for investors.

A man in a suit pointing at a drawing of a light bulb with a U.S. Dollar sign inside it.

IMAGE SOURCE: GETTY IMAGES.

The announcement of Milligan's departure overshadowed several aspects of Gilead's transition to a "new" company. Most important, sales for the biotech's hepatitis C virus (HCV) franchise appear to be stabilizing. This is key because the focus for Gilead and investors should switch to other areas. One of those areas is Gilead's renewed strength in HIV treatment, led by powerhouse drug Biktarvy. Another is the biotech's quiet dominance in cell therapy. 

However, I think that Gilead's pipeline could be the most overlooked story for the company. Gilead should claim blockbusters in the not-too-distant future in two highly lucrative arenas: immunology and nonalcoholic steatohepatitis (NASH).

The biotech expects to soon announce results from a phase 3 study of filgotinib in treating rheumatoid arthritis. Approval for the indication could translate to peak annual sales between $2 billion and $3 billion. Gilead also hopes to file for approval of NASH candidate selonsertib in the second half of 2019. Some observers have dubbed the NASH market "the next hepatitis C."

In the meantime, Gilead stock trades at less than 11 times expected earnings. Its dividend yields more than 3%. I think Gilead's shifting gears will mean acceleration in the coming years.

A leader in the often-neglected area of mental health

Chuck Saletta (Magellan Health): While it doesn't get as much attention as the search for the next great genetic therapy, mental health remains an important part of people's overall well-being. Around 1 in 10 Americans are covered by some aspect of Magellan Health's overall services, making it a giant in the field of mental health treatments.

That's a pretty strong level of coverage from a business that you may never have heard of before. The fact that it flies somewhat under the radar makes it easier for the market to ignore the business too, and that's part of the reason why Magellan Health looks like a candidate to consider buying right now.

Its shares recently traded hands at around $75 per share, which is not that far above its 52-week low. Despite being unloved by the market, Magellan Health is starting to look attractive to value-oriented investors, as it trades at around 11 times its expected forward earnings. Perhaps even better, those earnings are anticipated to grow at a nearly 9% annualized rate over the next five years, which provides a reason to believe its shares could recover.

The company's solid balance sheet provides a decent backstop to its shares as well. It trades at around 1.4 times book value, meaning it has assets to back up its market price. In addition, its debt-to-equity ratio is around 0.6, and it has a current ratio around 1.6. That combination means that even if its business does stumble temporarily, it should have the wherewithal to recover.

Decent values on solid businesses don't last forever, which makes now a great time to consider Magellan Health.

The tide may be turning for this biotech giant

Todd Campbell (Celgene): A series of high-profile stumbles caused Celgene's shares to tumble, but several catalysts are fast approaching that could rekindle interest in this big-cap biotech.

Celgene's plans to further diversify itself by winning FDA approval for its multiple sclerosis drug, ozanimod, were delayed when the FDA sent its application for approval back for fixes earlier this year, but management's on track to refile that application early next year.

Additionally, Celgene's got four other potential blockbuster approval decisions coming by the end of 2020. Earlier this year, it acquired rights to fedratinib, a myelofibrosis drug it plans to submit for approval by the end of 2018. The company also acquired rights to the cancer gene therapy liso-cel earlier this year, and it could win an FDA go/no-go decision in 2019. An application is expected next year for luspatercept, a beta thalassemia and myelodysplastic syndromes drug that Celgene thinks could be a billion-dollar blockbuster, and collaboration partner bluebird bio (NASDAQ:BLUE) could win an FDA OK for the multiple myeloma gene therapy bb2121 in 2020.

A lot of shots on goal should help the company deliver on its 2020 forecast for sales of at least $19 billion and earnings per share of $12.50. For perspective, it's currently guiding for sales and EPS of at least $14.8 billion and $8.70, respectively, in 2018.

Celgene's Revlimid and Pomalyst remain dominant first-line and third-line multiple myeloma drugs, and label expansions into new indications and for new multidrug combination therapies should help them maintain their market share. The company's psoriasis drug Otezla and its pancreatic cancer and breast cancer drug, Abraxane, should remain top sellers too.

Overall, Celgene's price-to-sales and price-to-earnings ratios are near their lowest since 2012, making buying it now ahead of these upcoming events especially intriguing.

Chuck Saletta has no position in any of the stocks mentioned. Keith Speights owns shares of Celgene and Gilead Sciences. Todd Campbell owns shares of Bluebird Bio, Celgene, and Gilead Sciences. His clients may have positions in the companies mentioned. The Motley Fool owns shares of and recommends Bluebird Bio, Celgene, and Gilead Sciences. The Motley Fool has a disclosure policy.