A horrible disease, and insidious, and I don't blame the OP at all for being concerned for her brother-in-law. I lost my husband to cancer. My father had died of it too, so I should have noticed that he was getting thinner and had more indigestion than previously, but he didn't complain, or tell me of the tarry stools and the twinges in his colon. He was doing that man thing, suffering in silence and hoping it would go away. It took a poo-stick test to start the diagnosis, and by then it was in his liver and his lungs, and the two-and-a- half year prognosis turned out to be pretty accurate. For two and a quarter years of that our life was much as before, just the last bit was unpleasant, but we didn't see our golden wedding together, so the OP's sister and brother-in-law were luckier than us.
The thing is, every time it is referred to as the "big C" it reinforces the idea that cancer is unique, lethal and unmentionable, so it is not openly discussed, and that means that numberless people don't know accurately what the symptoms are and never see a GP until it has metastased and spread.
As an ordinary but potentially fatal illness like others (strokes, heart disease, MS, dementia, broken limbs, Parkinsons, tuberculosis - you can add dozens, and don't forget mental illnesses like depression too) no-one would be coy and whisper about it and diagnoses would be earlier and more effective.
The more open we are about it, the better, and perhaps we can catch and cure more cases. As it is, the 10 year survival rates for the most common cancers are 50%, and survival rates have doubled in the last 40 years. Those rates are listed at
www.cancerresearchuk.org/health-professional/cancer-statistics/survival