Scientists have created a laser-based platform that can quickly and noninvasively screen large quantities of blood in patients with melanoma to detect circulating tumor cells (CTCs) - a precursor to deadly metastases. The new system accurately sniffed out hard-to-detect CTCs in 27 of 28 patients with the cancer in as little as 10 seconds and was 1,000 times more sensitive than existing assays (detecting one CTC per liter of blood). Although more work is needed, the test could help identify patients at risk of metastasis and guide the use of laser therapies to kill melanoma cells. Researchers have attempted to assess CTCs to determine the risk of metastasis in patients, but existing assays can only examine small amounts of blood, which sometimes do not capture any CTCs. Seeking a solution, Ekaterina Galanzha and colleagues created a system called the Cytophone that uses laser pulses and focused ultrasound to noninvasively peer under the skin of patients with melanoma, revealing pigmented CTCs that pass through veins in the arm. Galanzha et al. applied their technology to 28 light-skinned patients with melanoma and 19 healthy volunteers and found that it identified CTCs in 27 (96%) of the patients between 10 seconds and 60 minutes without generating false positives in the controls. Importantly, the system's laser could destroy the detected CTCs, resulting in a large drop in CTC numbers. It also uncovered circulating blood clots - the second leading cause of death in cancer patients. The Cytophone was able to account for other variables such as patient skin pigmentation and movement, but future studies should investigate and expand on the range of skin tones for which the technology could be used.