Is psoriasis a contradiction for microneedling procedure?

The  recommended time in between treatments is 4-6 weeks. As this is enough time to allow your skin to heal and the collagen production to take effect. You can do them in  3 week intervals if you feel it’s necessary and are in a rush to complete your treatments. 

There is no maximum number of sessions, and no correlation to cancer or malignancy.  Acne scars can be difficult, and may require multi-modality treatment to achieve results.  11 sessions is quite a few, and if not getting the results you expect I would consider other options....

At my practice we often do this treatment on the forearms and hands.  It will take several treatments to see the results you desire.  In addition to doing microneedling, I would suggest using 2 syringes of radiesse in the hands.  One syringe per hand.