When is the appropriate time to consider euthanasia for a cat diagnosed with feline oral squamous cell carcinoma?

The appropriate time to consider euthanasia for a cat diagnosed with feline oral squamous cell carcinoma is when the cat's quality of life is significantly impacted by the disease and their suffering cannot be effectively managed through other means. It is important to consult with a veterinarian to assess the cat's condition and discuss the best course of action.