 DexCom Inc. DXCM, 1.39 shares fell nearly 17 in the extended session Thursday after the maker of glucose monitoring systems missed analyst expectations for its first quarter and tweaked higher its 2022 revenue outlook. DexCom said it earned 51 million, or 12 cents a share, in the second quarter, compared with 78.4 million, or 19 cents a share, in the year-ago period. 