Breast screening call back for further tests

Hi all.  I had my routine mammogram recently and received a call-back letter this morning asking me to come for more tests at the assessment clinic in a few days time.  When I had my previous mammogram 3 years ago they found a lump, did an ultrasound and took a core biopsy.  It turned out to be a benign fibroadenoma and they left a marker in my breast for future examinations.  I don't know whether the call back is related to what they found last time or something new.  Anyway, I am trying not to worry too much (easier said than done as we know!) but I have a couple of questions that perhaps someone who's been in a similar situation might be able to answer.  Firstly would they call me back just because of the fibroadenoma that was already discovered last time, even though there was a marker and they already know about it?  Just to check it maybe?  And secondly, can a fibroadenoma develop into cancer?  I'm 54.  Thanks in advance.