Egg-shaped cameo valuable, to some extent (4)

I believe the answer is:

oval

'egg-shaped' is the definition.
('oval' can be a synonym of 'egg-shaped')

'cameo valuable to some extent' is the wordplay.
'to some extent' says the answer is hidden in the clue.
'OVAL' is hidden within 'cameo valuable'.

(Other definitions for oval that I've seen before include "Elliptical - cricket ground" , "Ellipsoidal" , "Ellipse" , "Cricket ground - presidential office" , "Stretched circle?" .)

I've seen this clue in The Times.

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