When should unexpected weight loss warrant further investigation to exclude cancer?

I accept the general thrust of the article , but I question the advice to "patients" as yet another example of ensuring that this latter role should apply even to those who are fit with no other symptoms. We need good evidence on significant outcome benefits , the burden of unnecessary investigation and opportunity costs for the GP. Surely unintended weight loss ( even of the 5% suggested elsewhere in the article) , has not been shown to be always " abnormal” in those with no other symptoms. A common enough occurrence in older patients taking advantage of retirement is to take up fresh activities often becoming absorbed enough to miss meals and coinciding with an age related loss of muscle mass. Those enjoying activity may drive themselves far harder than those just trying to lose weight. A healthier diet with fewer high calorie foods may also be part of this .I recall that my first short term weight loss of > 5% was as a medical registrar also engaged in research with very irregular hours. Perhaps looking at working conditions would have been more appropriate than assuming a remote chance I might have of significant underlying disease. Given a repeat of those circumstances I would still not see seeking medical advice as my first option. With ageing I have learnt that one is rarely free of additional symptoms but have still declined to seek medical advice for any weight loss which I have from time to time and become a "patient" for this.