According to a CNN article on July 17, Justice Ruth Bader Ginsberg had been undergoing chemotherapy to treat a recurrence of cancer.
The CNN article states that according to Justice Ginsberg's official statement on July 17th, she was admitted to Johns Hopkins Hospital in Baltimore due to the recurrence of her cancer after a recent periodic scan discovered lesions on her liver. The full statement released by the Supreme Court press stated that the Justice started to undergo cancer treatment in May 2020 after a period scan in February revealed lesions on her liver. Justice Ginsberg's statement further indicates that a recent scan (July 7th) showed a significant reduction in lesions and no new disease. The statement also expresses that the Justice will be able to continue in her post in her full capacity.