The "check 'em Tuesday" campaign is a weekly call for women to examine their breasts. Readers are asked to send in photos to prove compliance and can even sign up for a text message reminder.
But Dr McCartney argues that teaching women to examine their breasts regularly "has been shown not to reduce deaths from breast cancer and actually increases the chances of a benign biopsy result." She says it is "unfair to tell women that regular self examination will save their lives when it may simply incur anxiety and have the potential to harm."
She points out that this is just one aspect of a bigger move to promote untested "breast awareness."
For example, the charity Breakthrough Breast Cancer, which is not connected to The Sun's campaign, tells women to "touch, look, feel" regularly and advocates "knowing what your breasts look and feel like normally" as well as being able to name "the 5 signs of breast cancer."
NHS Choices suggests that women should examine their breasts at different times of the month in the shower or bath and lists nine changes to "look out for" and to "look and feel."
The charity CoppaFeel, which is involved with The Sun's campaign, offers text message reminders to prompt women to do a regular self examination.
Dr McCartney argues that public health messages "should be based on evidence" and that their effects "need to be proved to affect behaviour in a way that is helpful and not harmful." She says: "If we fail to critically evaluate campaigns on cancer, we create the appearance of doing something useful while potentially distracting from what might really help. In doing so we potentially harm the very women we're purporting to help." The Sun's primary interest is in selling papers; so what are the charities' and the NHS's excuses, she asks?