Oh you are so correct.
People do not get it....my wife is battling a very aggressive type of breast cancer and I, like you, find myself avoiding some situations where there will be conversations about her plight.
Some very helpful (not!) comments have been,
"my auntie died of breast cancer it was terrible"
I have been in a situation where work collegues have suggested that it is the near by radio towers that caused it and they continued on with this conversation in front of me for a few minutes.My personal favourite was a letter from a church group explaining why god does this and the power of Prayer. I am not religeous so why they bothered is beyond me.
I have had close friends fall off the radar completely and people feeling it is o'k to discuss the situation in front of my children.
I am so sorry for your loss and do empathise with you.....People really don't get it.