> I truly hope cancer will meet its "penicillin" one day (yes I know this is unlikely).

Penicillin blocks a specific enzyme (transpeptidase).

https://en.wikipedia.org/wiki/Penicillin-binding_proteins

Cancer cells, by definition, are not a uniform mass. It will depend on the cancer type, which in turn is defined by the properties those cells have. And mutations happen all the time, often more in cancer cells when their repair systems also have mutations, e. g. are less efficient. By that definition alone, there can never be a wonder-cure for all cancer types. At best you can find some proteins more important (p53 for instance) and while more than 50% of cancer cells have some form of mutation in p53, others simply don't. By that definition there will never be a penicillin-equivalent to all cancer types.