The beauty of ThermoDox isn't that it's a new drug - it's a new delivery. Celsion has taken doxorubicin, which is already a proven treatment against multiple cancers, and wrapped a heat-activated liposome around it. The affected (cancerous) area of the body is heated, causing the drug to be activated directly at the tumor's location. As such, it's made more effective.
In any case, the question here isn't one of market size - it's a question of efficacy. Will the Thermodox test on liver cancer be good enough to continue forward with the testing. For most drugs that make it to Phase III, the answer is yes, and for fast-tracked drugs like this one, it's usually a strong yes.