Perhaps that's an odd question to ask. I don't like thinking of people as being cancerous, but sometimes actions and attitudes do keep a church from becoming as healthy as God intends.
The idea came to my mind because of a comment a friend made a few days back. He told of a person who claimed that I had used the word "cancer" to describe members of his family many months ago. I didn't. I actually used that word to describe people from a completely different family whose actions and attitudes were crippling our ministry and undermining our senior pastor. Sounds cancerous to me.
But I guess even USING a word like "cancer" in a conversation is risky. Someone can misunderstand and misinterpret the main message being communicated. I certainly learned that!