My husband is a pretty big guy. He's about 5'10" and weighs in around 225. Or did. In the pre-cancer days.
Cancer in general and pancreatic cancer in particular tend to cause weight loss. This happens for a host of reasons. For starters, many cancer treatments make you lose your interest in food. You're either nauseous, fighting diarrhea, have gas, get pain from spicy food, or food just doesn't taste as good as it used to. GH has often reported that things "just taste funny." Some drugs cause food to taste metallic. In any case, chemo has a direct negative impact on many a patient's interest in eating.
Then there's the "wasting," or cachexia. Basically, the cancer changes your metabolism and you lose muscle and fat even though you're eating reasonably well. There are studies that show that fish oil supplements can help prevent/slow this syndrome. GH is a big consumer of fish oil, yum.
Until recently, GH had pretty much maintained his weight. With the recent diarrhea developments, he's starting to lose ground. He's down to about 200, a decent weight, but with his clothes starting to hang off of him he looks sickly in a way that hasn't been true before. And I feel like the wasting has set in. His arms and legs are shadows of their former selves. It's scary. And sad. In all this time, he's never really looked sick before, and now he does, although probably not to the casual observer. But I see the difference. And it makes me very, very nervous.