You've nailed it, @Tri - it is the limitations of mammograms particularly for those diagnosed with ILC that are at even more risk of not being diagnosed - as ILC doesn't 'present' as lumps - it is more like 'strands' - and it is usually slow growing. It may have been there for years & missed on every mammogram, until, in my own case, my GP found it on a random manual check (even tho I had a clear mammogram just months before.) She had a standard procedure of doing both Breast and Pap smear checks at the same time.
Lumps are hard enough to detect with dense breast tissue, let alone thin strands! Hence the need for being advised of breast density early in the piece & ultrasound to be standard follow up procedure once it is identified on the mammogram.
I've added ILC & missed mammogram to the possible 'poll'! ;)