Calypso Medical Technologies, which is being sold for little more than $10 million, will go into the books as a technological success for patients but a financial black eye for its backers.

The Seattle company raised more than $150 million from investors since its founding in 1999. The sale to Varian Medical Systems, announced Monday, came after Calypso was unable to raise additional money to expand its tool for tracking the position of tumors during radiation therapy and other treatment, said Joseph Piper, of Seattle's Integra Ventures, one of Calypso's earliest backers.

"It's a disappointing result, to say the least," he said.

"It will live on, and people with prostate and lung and other terrible cancers will have something that was created in Seattle," he added. "There's a lot that got accomplished in that company, and someone is going to make a lot of money. Unfortunately it's not going to be the legacy shareholders."

Calypso CEO Edward Vertatschitsch said the company currently employs more than 100, and will continue its R&D and manufacturing operations here. It's too early to say exactly what future staffing levels here will be, he said.

The deal includes about 90 current or pending patents. Calypso's investors could get additional payments from Varian, a leading provider of cancer technologies, if its sales top certain targets in the next 2 ½ years.

Earlier this year Calypso raised $7.5 million, but its big capital infusions came in two-year intervals during the previous decade: a $50 million round led by Frazier Healthcare Ventures, of Seattle, and Skyline Ventures, of Palo Alto, in 2009, $42 million in 2007, and $44 million in 2005. That money followed about $33 million in earlier funding, according to reports at the time.

The company won approval from the Food and Drug Administration as well as European regulators for its so-called "GPS for the Body" system, in which a tiny transponder is implanted into a prostate tumor so that radiation therapy, radiosurgery and other treatments can be precisely targeted.

It has begun European clinical trials, and is gearing up for U.S. testing, for clinical trials of the system in lung cancer, Vertatschitsch said.

Revenues are running at an annual rate of $15 million, and Calypso has installed more than 110 systems in North America and Europe, the company said. Its tracking system has been used in treating an estimated 10,000 prostate-cancer patients.

But in the current investment climate, said Piper, Calypso's recent backers weren't ready to commit the additional capital needed to build out a sales team for its existing products and to fund further clinical trials.

By contrast, Varian "can use all of its strength to take the technology forward and broadly apply it," Vertatschitsch said. "They are expecting to invest in the technology and take it the final mile."