By Nate Raymond

BOSTON, June 5 (Reuters) - A Massachusetts judge ruled that two doctors may move forward with a lawsuit seeking an order that the state's murder and manslaughter laws do not apply to physicians who offer lethal medications to terminally ill patients.

Superior Court Judge Mary Ames in Boston in a ruling last week declined to dismiss the lawsuit by the doctors, one of whom is suffering from cancer, who argued a cloud of uncertainty was preventing physicians from providing such medications.

The doctors have proven there is a controversy regarding the law that is worth the court's time to consider, Ames said in the decision, noting that she had not yet made a determination on the merits of their argument.

The lawsuit aims to include Massachusetts among states such as Oregon, Washington, Vermont, California and Colorado and the District of Columbia that allow physicians to provide aid in dying, according to right-to-die advocates.

The Massachusetts ruling was in response to a lawsuit by Roger Kligler, a retired doctor diagnosed with stage-four prostate cancer, and Alan Steinbach, a physician who says he is willing to write prescriptions for lethal medication but fears prosecution.

The lawsuit seeks a ruling holding that manslaughter charges cannot be applied to physicians who write a prescription to terminally ill competent adults who request medication that they could choose to self-administer to aid in their death.

"We are pleased with the court's decision because it will allow our clients to challenge the constitutionality of the law without having to take actions that could risk prosecution by an aggressive district attorney," said John Kappos, a lawyer for the plaintiffs, said in a statement.

A spokeswoman for Massachusetts Attorney General Maura Healey, who was named as a defendant along with the Cape and Islands County district attorney and is defending the case, declined to comment.

Healey's office had in court argued the court should defer to the state legislature to decide the issue and ensure safeguards are enacted to protect vulnerable patients and the integrity of the medical community.

The lawsuit is being pursued by nonprofit right-to-die organization Compassion & Choices.

The Massachusetts legislature has considered, but never enacted, legislation to allow physicians to provide aid in dying. In 2012, voters narrowly defeated a ballot initiative that would have legalized the practice. (Reporting by Nate Raymond; Editing by Scott Malone and Andrew Hay)

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