If I am suffering from a deadly disease and there is a cure which may work and may not work and I refuse to take the treatment, will that be considered as an act of suicide?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Refraining from seeking medical treatment is not considered suicide at any rate. The Encyclopedia of Fiqh reads, "The majority of the scholars held that refusing treatment when one is sick is not considered suicide. A sick person who refuses treatment until he dies is not considered sinful, because it is not certain that this treatment would cure his sickness..."

It is worth mentioning that some scholars held that treatment is obligatory if refusing it leads to death. However, this is in the case in which it is known with certainty that this treatment would cure the sickness by the permission of Allah. If the treatment may or may not work, as mentioned in the question, then it is not an obligation to take it.

Allah knows best.