Many investors pay attention to mid-cap stocks because they have established business models and expansive market opportunities. However, their paths to becoming $100 billion corporations are ripe with competition, ranging from giants with vast resources to agile upstarts eager to disrupt the status quo.

This is precisely where StockStory comes in - we do the heavy lifting to identify companies with solid fundamentals so you can invest with confidence. That said, here are two mid-cap stocks with massive growth potential and one that could be down big.

One Mid-Cap Stock to Sell:

Biogen (BIIB)

Market Cap: $17.85 billion

Founded in 1978 and pioneering treatments for some of medicine's most complex challenges, Biogen (NASDAQ:BIIB) develops and markets therapies for neurological conditions, including multiple sclerosis, Alzheimer's disease, spinal muscular atrophy, and rare diseases.

Why Do We Steer Clear of BIIB?

1. Customers postponed purchases of its products and services this cycle as its revenue declined by 7.4% annually over the last five years

2. Projected sales decline of 7.3% over the next 12 months indicates demand will continue deteriorating

3. Earnings per share decreased by more than its revenue over the last five years, showing each sale was less profitable

Biogen is trading at $122.47 per share, or 7.6x forward P/E. Check out our free in-depth research report to learn more about why BIIB doesn’t pass our bar .

Two Mid-Cap Stocks to Watch:

Comfort Systems (FIX)

Market Cap: $15.32 billion

Formed through the merger of 12 companies, Comfort Systems (NYSE:FIX) provides mechanical and electrical contracting services.

Why Do We Love FIX?

1. Average backlog growth of 30.5% over the past two years shows it has a steady sales pipeline that will drive future orders

2. Earnings growth has massively outpaced its peers over the last two years as its EPS has compounded at 68.2% annually

3. Returns on capital are growing as management capitalizes on its market opportunities

Comfort Systems’s stock price of $444.72 implies a valuation ratio of 23.3x forward P/E. Is now the right time to buy? See for yourself in our in-depth research report, it’s free .

Centene (CNC)

Market Cap: $29.75 billion

Serving nearly 1 in 15 Americans through its government healthcare programs, Centene (NYSE:CNC) is a healthcare company that manages government-sponsored health insurance programs like Medicaid and Medicare for low-income and complex-needs populations.

Why Could CNC Be a Winner?

1. 15.5% annual revenue growth over the last five years surpassed the sector average as its offerings resonated with customers

2. Dominant market position is represented by its $169.3 billion in revenue, which gives it negotiating power over membership pricing and reimbursement rates

3. Earnings growth has trumped its peers over the last five years as its EPS has compounded at 14.8% annually