Invion Limited announced the results from the latest Proof-of-Concept (PoC) studies undertaken by its research partner, Hudson Institute of Medical Research. This pilot study used INV043 to treat immunocompetent mice that had been implanted with triple negative breast cancer (TNBC). TNBC is an aggressive and metastatic tumour type that is innately resistant to most chemotherapies. These tumours are difficult to treat and have high mortality rates. Results showed a complete regression in the tumour and appeared to have triggered an immune response that subsequently prevented the recurrence of TNBC. The latest studies follow on from the initial successful PoC tests announced on 25 May 2021 which used immune-deficient mice.Testing Approach: TNBC cells were implanted, establishing solid tumours in the mammary fat pad that rapidly metastasised. The treatment group (n=3) with established tumours had INV043 injected intratumorally, and subsequently were illuminated with red light. No anaesthesia was required and no adverse effects were observed. Treatment was repeated nine days later. There were three control groups. One was made up of untreated mice, while the remaining two groups consisted of mice that were either administered with light or with INV043 alone. Details of Results: PDT treatment using INV043 resulted in complete tumour regression with no recurrence of disease. Moreover, there was no apparent scarring or other indication of prior tumour presence, and no evidence of either primary tumour or metastatic spread at autopsy. As a preliminary probe of immune-mediated effects, mice that achieved remission were re-challenged by a second implantation of TNBCs at a new site. No new tumours could be established, suggesting the successful development of protective immunity following INV043 treatment, a key requirement to maintain long-term remission. In the control groups, tumours enlarged rapidly and had reached endpoint (tumour size >100mm2) by day 19 with autopsies showing the cancer had spread to the lungs and the abdominal fat pad. Control animals that received only INV043 or light treatment showed similar progression. Further PoC studies by Hudson Institute are ongoing, including a larger TNBC study (primary tumour model), as well as secondary study investigating the potential of INV043 to treat metastatic disease. Each study will include arms exploring potential synergies with other cancer therapies. As indicated, there were three mice (n=3) in each of the four groups (treatment, light control, INV043 control, untreated). Thus, the total population size of the pilot study is 12. There was no significant difference in tumour size between any group until day 19 of tumour growth (four days following treatment #2), when tumour size reduced substantially in treated animals compared to all control groups. The sample size is too small for the p-value to be considered relevant, but as requested in the interests of additional disclosure, significance between groups was calculated using one-way ANOVA with Tukey's multiple comparisons test.