It mutated into the Partito Democratico della Sinistra, a wishy-washy name if there ever was one, and greatly reduced over time its Marxist component. By doing so, it reached the power.
During the Lead Years, the Brigate Rosse terrorist group enjoyed some support from within the ranks of the PCI.
All in all, from the end of WWII onward the party was one of the backbones of the Italian political scene, not to mention the fact that it was the only one able to produce good political satire (which excludes Forattini, by definition).
It was the party of Palmiro Togliatti, Enrico Berlinguer and Gramsci. It had and has a major influence in Unions; of course, during the Fascist regime it was repressed and its leaders and militants either took to exile or were imprisoned. Or killed.
The italian Resistenza movement was largely a Communist movement, although there was also a Catholic and Liberal presence.