Italian, 16th century.
Mounted in an unmarked high carat gold brooch setting which dates to the 19th century.
The cameo measures 3.1 x 2.4cm.
Similar cameos, also dating to the 16th century can be found in the Royal Collection Trust, Inventory Numbers; RCIN 65854 and RCIN 65859.
Further examples can be found in ‘The Marlborough Gems: Formerly at Blenheim Palace, Oxfordshire’, page 252 and 253, figs 586 and 588.
Links;
https://www.rct.uk/collection/search#/19/collection/65854/a-young-woman
https://www.rct.uk/collection/search#/18/collection/65859/a-young-woman