A retired Falmouth doctor’s right-to-die lawsuit may have gotten a bit more complicated, but for good reasons.

Defying the odds, Dr. Roger Kligler’s most recent blood tests show the levels of his metastatic prostate cancer have significantly declined, opening up the possibility that he could possibly live for many unexpected years.

The news comes as he prepares to attend his first court hearing on his right-to-die lawsuit this week.

Despite his oncologists’ prediction that he probably has years to live, Kligler, 65, is reflexively cautious. His 15-year up-and-down struggle with the disease has left him suspicious of good news. But even he is embracing the possibility of a longer life. The news comes amid other recent glad tidings, including the marriage celebration of his daughter and the birth of his first grandchild.

“You come to peace that you’re at the tail end of your life,’’ he said. “Then all of a sudden, it’s like a reprieve.’’

Kligler and his lawyers say they remain as impassioned as ever about expanding “medical aid in dying’’ options throughout the country, but Kligler’s more upbeat prognosis could make him a less dramatic public figure in the right-to-die movement. It could also alter the tone of his pending case.

In the original complaint filed in Suffolk Superior Court about four months ago, lawyers for Compassion & Choices, a nonprofit right-to-die organization working with Kligler, wrote that his “medical conditions are worsening’’ and called for “expedited court scheduling.’’ A later court filing said, “Time is short for Dr. Kligler.’’

John Kappos, one of his lawyers, said that Kligler’s test results may lift the urgency for some court decisions but insists that Kligler remains a forceful and appropriate plaintiff, a man with an unpredictable, life-threatening disease. Last Friday, he gave written notice to the parties in the case about Kligler’s improved medical condition but emphasized that Kligler“is still diagnosed with a terminal illness.’’

He said the fundamental aspects of their lawsuit remain unchanged: They want a judge to declare that “medical aid in dying’’ is not a criminal offense in Massachusetts and to bar top prosecutors from bringing homicide-related charges against any doctor who takes part in this type of death.

Named as defendants in the case are Attorney General Maura Healey and Cape and Islands District Attorney Michael O’Keefe, who have authority over the jurisdictions where Kligler and the other plaintiff — Dr. Alan Steinbach, a Cape Cod doctor who wants the option to prescribe the necessary medication to Kligler or others who seek to accelerate their death — reside.

In court papers filed two months ago, Healey and O’Keefe asked the judge to dismiss Kligler’s case, saying it is premature because nothing has happened to warrant any intervention and they have no conflict with him or Steinbach at this time. They also went out of their way to express sympathy for Kligler’s condition and said the lawsuit raises highly controversial issues that should be decided by the Legislature.

Kligler and his lawyers, however, say they have little reason for optimism in the legislative process. A “compassionate aid in dying’’ bill has languished for the past eight years, and a 2012 ballot initiative also failed, though by a narrow margin. Opponents argued that the measure, which they call “physician-assisted suicide,’’ violates a doctor’s Hippocratic Oath to “first, do no harm’’ and would set a dangerous legal precedent.

In its search for alternatives, Compassion & Choices began looking at Massachusetts laws and concluded that no homicide statute actually prohibits medical aid in dying. It also interpreted the state Constitution as protecting the right to such deaths under extreme circumstances.

The group endorses “medical aid in dying’’ options that would allow physicians to prescribe fatal drugs to patients who are deemed mentally competent and have less than six months to live. The patient then has the option to self-administer the drugs at a time of their choosing.

Kligler said that he remains unwavering in his conviction that these end-of-life options should be available to terminally ill patients throughout the country. Currently, it is authorized in six states — Oregon, Washington, Vermont, Montana, California, and Colorado — and Washington, D.C., said a spokesman for Compassion & Choices.

The nonprofit group has had some success through the courts. It brought a similar legal case in the Montana courts, and although it prevailed about a year later, it was too late for the central plaintiff: Robert Baxter, a truck driver and Marine veteran, died of leukemia hours after the court decision.

Kligler emphasized that although he has a terminal illness, he has never been deemed “terminally ill,’’ typically defined as someone likely to die within six months. In court papers filed last fall, Kligler’s lawyer said his median life span, given his diagnosis and treatment, was about two years, with a range of seven months to six years.

But that was before his recent blood test for PSA, an antigen produced by the prostate that can at some levels indicate cancer. As of last week, his level had declined to 0.14, less than half of what it was six months ago.

In late November, when his PSA level had declined to 0.2, an oncologist at Dana Farber Cancer Institute in Boston, Dr. Isaac Klein, told him, “The short story is — I think you’re doing fantastic right now.’’

Any PSA level, however small, is still a sign of cancer for Kligler, even if normalfor many men. His prostate gland has been surgically removed, so his PSA level should be zero, he said. Any level suggests stray prostate cancer cells moved to other areas of his body, which are producing the PSA.

His bone scans previously showed cancer in his pelvic bones, but overt signs of the disease there have disappeared with radiation.

Since being diagnosed 15 years ago, he has also undergone surgery, hormone therapy, and immunotherapy, all of which came with debilitating side effects. Twice he got his PSA to zero; but over time, the level always crept back up.

Meanwhile, Kligler said he looks forward to this week’s court hearing as another opportunity to push forward the issue that is the passion of the final chapter of his life: seeing compassionate “medical aid in dying’’ options come to Massachusetts.

Though Kligler considers himself a highly private person, he said he has adjusted to his new role as a plaintiff in a high-profile case, including the speaking engagements and interviews that come with it. He said he wants to be part of a movement that recognizes the realities of death without taking away the joys of living.

For him, the happy times include relaxing walks on the seashore with his longtime wife, Cathy, volunteering to rescue stranded turtles, and helping deliveries at food pantries.

“I don’t want to die,’’ he said.

Patricia Wen can be reached at patricia.wen@globe.com. Follow her on Twitter at @GlobePatty.