Sigma-Tau SpA, the Italian drugmaker that’s developing rare-disease medicines, is considering selling a stake in the company after the death of founder Claudio Cavazza, said two people with knowledge of the situation. The closely held company is being advised by Milan-based Four Partners, said the people, who declined to be identified because the matter is private. While a sale of the entire company hasn’t been ruled out, the Cavazza family is leaning toward selling a stake in a deal that may value Sigma-Tau at about 1 billion euros ($1.4 billion), they said.