Recent blood tests suggest there is a "slight" possibility that Emperor Akihito may still have some cancerous tissue, despite having undergone prostate cancer surgery in January, his chief health official said Thursday.

"We see a slight possibility of the cancer remaining," Ichiro Kanazawa told reporters at the Imperial Palace, citing recent blood tests showing an elevated level of prostate-specific antigen.

"The cancer is not at such a level that it requires some special care immediately, so we will keep checking his condition until he is completely cured," said Kanazawa, who is in charge of medical affairs for the Imperial family.

High PSA levels in the blood may signal a prostate problem such as an infection, swelling of the prostate gland or cancer. A sharp PSA rise after prostate cancer surgery could mean a recurrence of cancer or that the cancer was not completely removed.

Kanazawa said he has also asked the Imperial Household Agency to reduce the Emperor's official duties, noting he will turn 70 in December.

While the Emperor's PSA numbers have remained low at two decimal places, they have been rising moderately and consistently in monthly blood tests.

Doctors cannot discount the possibility that cancerous tissue remains or specify any cause for the recent rise in the PSA level because the numbers are so low, according to Kanazawa.

When the Emperor was informed of his condition he reportedly told Kanazawa, "I want you to tell the people the truth."

The Emperor was diagnosed with prostate cancer last December after tests showed a rise in his PSA level.