OK, this a painful topic to go over, but I think it's a very bad run of awful luck that we've had at least three former female companions from the 1970s that have died in recent times.
Everybody's going to die eventually, but it's still troubling that Mary Tamm and Elizabeth Sladen died roughly two decades or so before the average Western life expectancy in their sixties. Caroline John also died at the somewhat older but still rather saddening age of 71. All from particularly nasty sounding cancers.
And another former female companion has been diagnosed with cancer recently (and I hope she pulls through).
Was it something the BBC put in its water? People have pointed at the possibility of asbestos used in the construction material.