Mass. Gen. Laws ch. 201D § 7
A principal may revoke a health care proxy by notifying the agent or a health care provider orally or in writing or by any other act evidencing a specific intent to revoke the proxy.
For the purposes of this section, every principal shall be presumed to have the capacity to revoke a health care proxy unless determined otherwise pursuant to court order.
A health care proxy shall also be revoked upon: (i) execution by the principal of a subsequent health care proxy, or (ii) the divorce or legal separation of the principal and his spouse, where the spouse is the principal's agent under a health care proxy.
A physician who is informed of or provided with a revocation of a health care proxy shall immediately record the revocation in the principal's medical record and notify orally and in writing the agent and any health care providers known by the physician to be involved in the principal's care of the revocation. Any agent or member of the nursing staff informed of or provided with a revocation of a health care proxy pursuant to this section shall immediately notify the attending physician of such revocation.
Mass. Gen. Laws ch. 201D, § 7