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What: Shares of department store giant Macy's (NYSE:M) dropped by 15% last month, according to S&P Capital IQ data. Investors weren't impressed with Macy's second-quarter earnings release on Aug. 12, and concerns are increasing that the company's current struggles could be a sign of greater trouble ahead.

So what: Macy's second-quarter results came in below Wall Street's estimates. Sales declined 2.6% to $6.1 billion, driven by a 1.5% decline in same-store sales. Earnings per share fell 20% to $0.64 per share, compared to analysts' estimates for $0.76, and net income plummeted 26% to $217 million. The poor results also led Macy's management to reduce its 2015 full-year sales outlook to down 1% from 2014, compared to its previous guidance for a 1% increase in sales. 

During the subsequent earnings call, management stated that increased competition and changing consumer shopping trends took a toll on Macy's results.

Now what: Macy's is taking a multipronged approach to combat these issues. It's closing underperforming stores, building out its online and same-day delivery capabilities, and exploring ways to monetize its valuable real estate holdings.

Yet the core problem is that Macy's, like other primarily brick-and-mortar retailers, finds itself on the wrong side of a powerful trend: the relentless growth of e-commerce. Juggernaut Amazon.com continues to take share in the apparel market, and that's a trend that's likely to continue for the foreseeable future. As such, Macy's remains a high-risk investment.

Joe Tenebruso has no position in any stocks mentioned. The Motley Fool owns and recommends Amazon.com. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.