The last five years have been an absolute dream particularly for biotech investors; shares of the iShares NASDAQ Biotechnology Index (ETF) (NASDAQ: IBB) have scorched the returns of the market over that time period, up more than 400% when the market itself returned a still-impressive 133%.

SPY Chart

While this outperformance is by no means unwarranted, given the strong financial performance of many of the large biotech stocks in the ETF, biotech investors would be right to wonder if biotech stocks' valuations may be slightly ahead of themselves.

Biotech stocks tend to be more volatile than the market in general, which can lead to wild price swings when the latter turns south. Long-term biotech investors shouldn't fear such crazy price movements; rather, we should look at them as opportunities to pick up shares in our favorite biotech stocks when the market is offering a discount.

Here are three stocks on my biotech shopping list that you can bet I will be buying if the market suddenly takes a turn for the worse.

First up on my list is the largest and most profitable biotech company in the world, Gilead Sciences (NASDAQ: GILD). Gilead offers biotech investors something quite rare in the sector, which is a stunningly profitable company with strong growth prospects selling at a below-market price-to-earnings ratio. Gilead's growth has been nothing short of stellar over the past several years thanks to the incredible success of its relatively newly launched Hepatitis C drugs Sovaldi and Harvoni. These drugs should continue to grow nicely in the years ahead. The most recent approval for sale of these drugs came from Japan, where there is a tremendous market opportunity for the Gilead to treat Hepatitis C patients.  

Source: Gilead.

Gilead also recently initiated a small dividend that currently yields 1.4% and has authorized a massive $15 billion share repurchase program that should continue to meaningfully bring down the share count. And yet, all of this good news is bundled in a company that trades for around 10 times 2016 earnings estimates. Any weakness in the share price would represent a great time for investors to consider opening up a position.  

Up next on my list is Celgene Corporation (NASDAQ: CELG), which is another biotech juggernaut that has been a massive winner in recent years. The company boasts a strong portfolio of products designed to treat a variety of disease states, but the bulk of its billions in revenue come from Revlimid, which treats multiple myeloma. Revlimid sales grew an impressive 16% in 2014, and contributed almost $5 billion in sales to the company's top line. When combined with other fast-growing drugs like Abraxane, which treats breast cancer, and Pomalyst/Imnovid, which, like Revlimid, also treats multiple myeloma, sales managed to grow by more than 18% last year.

Better yet, Celgene has been using its financial strength to buy back a significant amount of stock, which has reduced the share count significantly over the past few years. When combined with strong sales growth and cost control measures, margins have expanded company-wide, which has helped turbo-charge earnings-per-share growth.

CELG Average Diluted Shares Outstanding (Annual) Chart

Investors have been very excited about Celgene's recent performance, and the stock currently trades for around 40 times trailing earnings. While this isn't exactly what I'd call a cheap stock, the company does appear to have a very bright future ahead. The management team has given guidance for 2020 of sales over $20 billion and earnings per share over $12.50, which would represent huge growth when compared to last year's $7.5 billion in sales and diluted earnings per share of $2.39. If it achieves these results, the is stock is poised to do very well in the years ahead, and it could be a great buy if the market offers us a better price. 

Last on my shopping list is a company that has a bit more spice than Gilead or Celgene as it is not yet profitable, but it could hold more upside potential: Isis Pharmaceuticals (NASDAQ: ISIS). The company is developing a cutting-edge RNA-targeting technology that is used to inhibit the production of disease-causing proteins, and it boasts a pipeline full of potential. Isis curently has 38 drugs in its pipeline aimed at treating a wide variety of disease states, and eight of those drugs are currently in phase 3 clinical trials.

Isis has a who's who list of big pharma partners it has tapped to help finance the development and potential commercialization of these drugs. These partnerships have so far provided Isis with more than $1.4 billion in cash payments, and the company has the potential to earn an additional $8.5 billion in future milestone payments if it can successfully commercialize its pipeline.

Investors have certainly taken notice of Isis' progress and have bid up the stock accordingly, with the shares up more than 300% in the last three years alone.

ISIS Chart

While I'm more than happy to pay up for a company that is performing well, ISIS could make for a great investment if the market were to punish the stock for no good reason.

Any of these companies could make a fine investment choice, even at today's more elevated prices, as each holds great growth potential in the years ahead. Still, if Mr. Market were kind enough to offer us a substantial discount on any of them, you can bet I'll be more than happy to buy in at reduced prices.

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.