The 'It Feels So Good' singer underwent surgery at a private hospital in Harley Street, central London, at 7am Monday morning (15.06.09).
The 40-year-old star - whose real name is Sonia Clarke - discovered she had the potentially fatal disease last week.
Her spokesman Stuart Watts confirmed she was now receiving treatment, including yesterday's operation, as "a matter of urgency".
She is expected to remain in hospital until Saturday (20.06.09), and may be forced to cancel a number of summer concert dates, including an appearance the Danube Island Festival in Austria next week.
Sonique won the BRIT Award for British Female Solo Artist in 2001 and was hoping to release her new single 'World Of Change' next month.
The single release will be delayed if Sonique's health continues to deteriorate.
Sonique began her career in London reggae band Fari, before going on to sing with dance group S'Express in the 1990s.
She is the latest in a series of celebrities - including Kylie Minogue, Sheryl Crow, Anastacia and Olivia Newton-John - to battle the disease.
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