What is the test for a motion to amend the facts of a medical malpractice case?

Where the complaint fails to allege facts sufficient to state a cause of action and the trial court has sustained a demurrer without leave to amend, "we decide whether there is a reasonable possibility that the defect can be cured by amendment: if it can be, the trial court has abused its discretion and we reverse; if not, there has been no abuse of discretion and we affirm. [Citations.] The burden of proving such reasonable possibility is squarely on the plaintiff." ( Blank v. Kirwan (1985) 39 Cal.3d 311, 318, 216 Cal.Rptr. 718, 703 P.2d 58.)