Orevkov's four-cusp conjecture for plane rational cuspidal curves

Let $C\subset \mathbb{P}^2$ be a plane rational cuspidal curve, meaning a rational plane curve whose singularities are cusps. Orevkov's four-cusp conjecture. The curve $C$ can not have more than four cusps. This conjecture arises from the scarcity of examples of rational cuspidal plane curves with more than four cusps; the maximal number of cusps remains open in the source.