ABSTRACT Cutaneous metastatic breast cancer (CMBC) develops in up to 24% of patients with metastatic breast cancer. Systemic therapy often has limited efficacy in such cases, and surgery and radiotherapy offer only transient relief and their use may be limited in the CMBC population due to the side-effects involved and the extent of cutaneous lesions. CMBC can cause infection, bleeding, malodor and disfigurement and can progress to occupy large areas of the body. Kintara proposes a photodynamic therapy (PDT) known as REM-001 Therapy, wherein a photosensitive drug is injected into the body to collect at tumor sites, and is activated by a specially-designed laser focused on the selected lesions. The activated drug destroys tumors with minimal effects to surrounding tissue. REM-001 has been proven to be effective for many conditions, including CMBC. However, previous trials using a higher-than-threshold dose also reported high rates of unwanted side effects and longer healing time. In previous trials, symptoms such as eschar and ulceration increased recovery time and caused patients to leave studies but was not associated with better lesion outcomes. This project will reduce the treatment dosage to the previously identified threshold level – which demonstrated a 79% response rate in an initial study – in an effort to reduce side effects while still treating lesions. Kintara will test the reduced dose on 15 patients with symptomatic cutaneous lesions and stable systemic disease who are unable to receive surgery or radiotherapy at the time of treatment. These patients will be administered a single dose of REM-001 followed by light treatment and will be monitored for efficacy (lesion shrinking or disappearing, as well as pain and itch subsiding and improved quality of life) and safety/tolerability (eschar and ulceration, and bleeding and discharge from the lesions, treatment related photosensitivity, as well as standard clinical side-effect monitoring). Patients will continue on their existing standard of care systemic therapy and will receive it throughout the trial. If this trial is successful – the treated lesions shrink or disappear with the reduced treatment dose – Kintara will continue to a multi-site Phase III trial for CMBC and explore the use of REM-001 photodynamic therapy in other dermal indications.