A 22-person safety pilot tests a fluorescent spray designed to glow only on breast cancer

The surgeon finishes the lumpectomy. The tumor is out, but the question that drives the next thirty minutes is whether the margin, the rim of tissue around what was just removed, is clear. Today, that answer usually comes days later, from a pathologist. A phase I/II pilot whose protocol has just been published is designed to test whether a clear liquid sprayed into the surgical cavity can answer it in real time, by glowing only where breast-cancer cells remain.

The product is called AKRO-6qcICG, a topically applied, fluorescently quenched near-infrared imaging agent. It is the centerpiece of the SPRAYDYE trial, a single-center randomized pilot whose protocol was published in Frontiers in Surgery in 2026 (SPRAYDYE protocol, Frontiers in Surgery, 2026; indexed at PubMed 42558486).

Between 10% and 40% of patients who undergo breast-conserving surgery, the operation that removes a tumor while sparing the breast, end up with tumour-positive resection margins, the technical term for cancer cells found at the edge of the removed tissue. Such a finding usually means a second operation, or an extra round of boost radiation. The variability in those numbers tracks differences in tumor biology, in how pathologists define "close" versus "positive," and in how aggressively a given surgeon cuts. It is not a single-cause problem, and a fluorescent spray is one experimental lever, not a fix.

AKRO-6qcICG is what the field calls a "quenched" probe: a fluorescent molecule attached to a short peptide that keeps the fluorophore dark until a specific enzyme cleaves the peptide off. The enzyme the probe is tuned to is cathepsin, a family of proteases that breast-cancer cells overproduce on their surface and in their microenvironment. In healthy tissue, cathepsin activity is low, and the probe stays dark. In tumor tissue, cathepsin levels rise, the peptide is cleaved, and the probe fluoresces. A surgeon viewing the cavity through a near-infrared camera, picking up light outside the visible spectrum with a purpose-built detector, would see the glow only where the chemistry has been switched on.

The pilot is built to test that switch, and the protocol is explicit about what it is not testing. The primary outcome is safety: treatment-emergent adverse events in both parts of the trial. Part A enrolls six healthy volunteers, who receive blinded topical applications in two doses on suction blisters, with vehicle and untreated controls. Part B enrolls sixteen breast-cancer patients undergoing breast-conserving surgery, who receive a single topical dose in the surgical cavity after the tumor is removed. Secondary outcomes track local and systemic tolerability: wound healing, pain and pruritus on numeric rating scales, vital signs, ECG. No efficacy endpoint, whether sensitivity, specificity, or margin reduction, is in the design. The trial is not asking whether the spray works. It is asking whether the spray is safe enough to keep asking.

Most intraoperative molecular imaging probes in late-stage development are given intravenously, circulate for hours, and depend on a tumor's abnormal vasculature to accumulate. AKRO-6qcICG is applied topically into the open cavity. That shortens exposure, removes a systemic pharmacokinetic layer from the design, and changes the selectivity test. An IV probe has to find the tumor against the background of a living body. A topical probe has to find it against the background of a wound bed that already contains inflammation, blood, and disrupted stroma, all of which can also release cathepsins.

The earlier work that justified moving into people was ex vivo. Topically applied AKRO-6qcICG has already been shown to enable clear breast-cancer visualization and to detect tumour-positive margins in resected tissue, the paper notes. Ex vivo tissue is not a wound bed. The pilot is, in part, an answer to the question of whether the ex vivo signal survives contact with a living, bleeding, healing surgical site.

Twenty-two people will not settle whether real-time intraoperative margin feedback changes re-excision rates, radiation use, or survival. That would require a phase III trial with hundreds of patients and a clinical endpoint. The SPRAYDYE pilot is testing a narrower set of questions: can a topical, cathepsin-activatable probe be applied safely, tolerated locally and systemically, and detected at all by a near-infrared camera in a real operating room. If the answers are yes, the next study can ask the harder one.