Late last month, the execs at Millennium Pharmaceuticals were upset over monthly sales data reported by IMS Health, the big gorilla in the behind-the-scenes world of market research. Contrary to their own reports, IMS reported that sales of their Velcade treatment for multiple myeloma were down. This upset investors and, consequently, hurt Millennium stock. So the Millennium execs did something unusual - they fired back by filing a brief statement with the Securities and Exchange Commission that disputes the IMS data.

“While the company typically does not comment on IMS sales data, the company believes it is important to remind the public that there have been frequent and significant discrepancies in IMS data relative to actual Velcade sales. The company has noted these discrepancies on a monthly and quarterly basis, both in terms of direction and magnitude of change,” the filing states.

Millennium also apparently persuaded Wall Street analysts that IMS was off base. In an investor note issued earlier this month, Citigroup’s Yaron Weber wrote that IMS data “seems incorrect” and “we should not rely on this data” for the first quarter, because Millennium is seeing strong growth compared with last December. IMS data has either overestimated or underestimated sales in recent quarters, he added. “Considering the historical inaccuracies of script data,” wrote Chris Raymond, an analyst at Robert W. Baird, “we do not view this news as indicative of Velcade’s growth outlook.”

What might the picture really look like? Impact Rx, another research firm, says Velcade’s share has bounced around, while a rival med - Celgene’s Revlimid - is gaining share. In February, Velcade notched 22.5 percent of patients who saw a doc and received a treatment, compared with 29 percent for Revlimid (click to enlarge). But Impact’s general managing director, Alan Braverman, says Velcade’s fluctuating share doesn’t indicate a “meaningful or dramatic” shift.

Meanwhile, an IMS spokesman writes us to say that: “IMS subjects its data to rigorous operational, statistical and quality control processes, actively working with our clients to ensure the information they receive is the most accurate estimate of marketplace activity and of the highest quality. It is not unusual for IMS’s national-level sales data to differ from client-reported sales data. Many reasons exist for these differences, such as different reporting periods, the treatment of discounts and rebates, and differences in coverage. IMS is…working with Millennium to address this specific situation.” And no doubt, IMS is still charging Millennium for the privilege.