Key TakeawaysMacy's missed second-quarter revenue and comparable store sales estimates as the retailer faced a tough consumer environment.The biggest U.S. department store chain operator also lowered its guidance because of the drop in sales and the need for more promotions.Macy's shares tumbled on the news. Macy's (M) shares slumped Wednesday after the retailer's second-quarter sales declined and it lowered its full-year guidance on weak consumer spending and more promotions. The biggest U.S. department st ...