Hello,
I have had this happen once before with tumorspheres kept in culture for over one week. It is possible that the tumorspheres have remained in culture too long. We generally counted spheres after one week, so a lengthier culture can lead to attachment. From my understanding, some cells respond better to different types of non-tissue culture petri dishes and low attachment plates as well.
I hope this helps.
Sara
2014-11-11 13:02:15