When will an expert be allowed to give evidence in a medical malpractice case?

Generally, an expert may "base his opinion on any 'matter' known to him, including hearsay not otherwise admissible, which may 'reasonably... be relied upon' for that purpose. [Citations.]" (People v. Montiel (1993) 5 Cal.4th 877, 918 (Montiel).) Further, "the expert may explain the reasons for his opinions, including matters he considered in forming them. However, prejudice may arise if, ' "under the guise of reasons," ' the expert's detailed explanation ' "[brings] before the jury incompetent hearsay evidence." ' [Citations.]" (Id. at pp. 918-919.) The trial court's resolution of "disputes" between a jury's need to fully and properly evaluate an expert witness's opinion based in part on extrajudicial matters and a defendant's interest in avoiding

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substantive use of unreliable hearsay is left to the court's sound judgment. (People v. Cole (1956) 47 Cal.2d 99, 105.) While often an instruction to limit the evidence to the basis for the expert's opinion and not for its truth cures any hearsay problem, sometimes such an instruction "may not be enough. In such cases, Evidence Code section 352 authorizes the court to exclude from an expert's testimony any hearsay matter whose irrelevance, unreliability, or potential for prejudice outweighs its proper probative value. [Citation.]" (Montiel, supra, 5 Cal.4th at p. 919.)