[teruakohatu]

Just like many cancers, the cancerous cells spread and destroy vital organs.

Yes they can be removed, but if the cancer has already spread then it may be too late.

[ejb999]

so it can be visually very small, and still kill you?

Just like an iceberg I guess...

[pas]

my late dentist went skiing, got a nasty cough, died 2 weeks later, lung cancer. no symptoms before. just a seemingly fit and healthy normal weight 30-something guy with a wife and kids. (maybe he inhaled too much enamel dust or who knows, the point is that humans are very bad at noticing these things on themselves/others.)