FILE PHOTO: U.S. Supreme Court Justice Ruth Bader Ginsburg stands during the National Anthem at the U.S. Citizenship and Immigration Services (USCIS) naturalization ceremony at the New York Historical Society Museum and Library in Manhattan, New York, U.S., April 10, 2017. REUTERS/Shannon Stapleton/File Photo

WASHINGTON (Reuters) - U.S. Supreme Court Justice Ruth Bader Ginsburg showed little evidence of slowing down on Monday, issuing rulings in two business-related cases just 11 days before her 86th birthday and two months after undergoing lung cancer surgery.

The liberal justice, who was named to the court in 1993 and is now its eldest member, had missed oral arguments in several cases in January while recuperating from her Dec. 21 surgery, but returned to the bench on Feb. 19 and has been an active participant since.

Ginsburg has now authored four of the court’s 17 rulings in its current term, which started in October and ends in June, more than any of the eight other justices. During the weeks when she missed oral arguments, Ginsburg worked from home and participated and voted in cases by reading transcripts and briefs.

One of her opinions on Monday came in a copyright dispute that was argued in January when she was absent. In a unanimous ruling that handed a setback to the American music industry, the justices decided that lawsuits alleging copyright infringement can be brought only when the U.S. Copyright Office has officially registered the copyright, which can take months.

In the other ruling, Ginsburg wrote on behalf of a 7-2 majority in favor of railroad company BNSF Railway Co in a case concerning a workplace injury that was argued in November.

Ginsburg underwent a surgical procedure called a pulmonary lobectomy at Memorial Sloan Kettering Cancer Center in New York to remove two cancerous nodules in her left lung. In January, the court said her recovery was on track.

She has had other health issues in the past. Ginsburg was treated in 1999 for colon cancer and again in 2009 for pancreatic cancer. In 2014, doctors placed a stent in her right coronary artery to improve blood flow.

Ginsburg, appointed by Democratic President Bill Clinton, is viewed as something of a cult figure by U.S. liberals, known as “RBG” after the late rapper Notorious BIG. A documentary film and a Hollywood biographical movie about her were released last year.

If Ginsburg, one of the court’s four liberal justices, were unable to continue serving, President Donald Trump could replace her with a conservative, further shifting the court to the right. Trump has added two justices since becoming president in January 2017, cementing its 5-4 conservative majority.