Low Grade Glioma with other health issues

Last year my husband was diagosed with a demyelinating lesion on his T1-T4 area through an MRI and lumbar puncture.  This was six weeks post pancreas/kidney transplant.  At the time the only symptom was a tremor upon examination by his primary doctor when checking reflexes.  At the time, the neurologist adopted a "wait and see" approach and told him that the medications he was already on for the transplant would be the medications they would prescribe anyway.

Since that time, his symptoms have grown progressively worse with a pronounced tremor in his right leg and hand, he experiences numbness at night in both hands, has had difficulty swallowing and has temporary pain issues when going from sitting or laying down.  The MRI this year showed no growth, but a slightly ill defined pattern and they determined it could also be a low grade gangliogliomas or astrocytoma.  They want to continue with a "wait and see" attitude and asked him to come back in a year.

In December, he experienced a dangerously low immune system and is on anti-rejection drugs.  But after lowering his dose, he began to experience rejection and they took his anti-rejection drugs back.  My questions are if his immune system is low, will this create an environment the tumor can grow in more easily, should the tumor be biopsied to determine exactly what it is and is a year too long to wait for another MRI?

Thanks for your help.

[medicalquest]

One more question...could the fact that he is on anti-rejection medications that are lowering his immune system be masking a higher grade glioma by not killing off the cancer cells as quickly as they would in a normal immune system?