RBC Capital analyst Kennen MacKay attributes the selloff today in shares of Exelixis to April total prescription data from Symphony. The analyst notes, however, that his analysis indicates the Symphony totals for April are well below those of IMS, implying prescription declines from March to April are not seen in IMS data. While the flat month-to-month growth from may be viewed as concerning for Cabo's continued uptake in first-line renal cell carcinoma post approval and launch of competitor Opdivo plus Yervoy in mid-April, March represented an "especially strong month," MacKay tells investors in a research note. He remains a buyer of Exelixis shares on today's weakness.