Madonna kicks off her "Sticky & Sweet" world tour at Cardiff's Millennium Stadium on Saturday, the latest test of her enduring appeal that comes a week after her 50th birthday. The "queen of pop" will be hoping to eclipse her last trot across the globe in 2006. "Confessions" became the top-grossing tour ever by a female artist with ticket sales of $195 million. "Sticky & Sweet," featuring hits that span nearly 30 years in pop music including her latest album "Hard Candy," includes 49 dates and is due to wrap up in Sao Paulo on December 18. As of Thursday, roughly half the tour venues had yet to sell out including Cardiff, although Live Nation announced in June that the tour was on target to gross more than $250 million. "Sticky & Sweet" is also a major test for Live Nation, the tour company that signed Madonna to a 10-year contract in 2007 reported to be worth a total of $120 million. Record label executives, smarting as some top acts jump ship to sign new deals with the likes of Live Nation and coffee chain Starbucks that reflect changes in the music industry, wonder if companies are paying too much to attract household names. Madonna reinforced her reputation as a shrewd businesswoman by switching from long-term label Warner Brothers at a time when the pop world recognized that live performing was generally more lucrative than selling records. Illegal downloads and competition from other forms of entertainment like video games have eroded music sales, and rising legal digital sales have failed to make up the shortfall. Ups and downsMusically, Madonna has few if any real rivals. The Recording Industry Association of America has described her as the best-selling female rock artist of the 20th century and the second top-selling female artist in the United States. Guinness World Records list her as the world's most successful female recording artist of all time and she has sold around 200 million albums. The Sunday Times estimates Madonna and husband Guy Ritchie's fortune at around $600 million. The last few years have not all been easy for Madonna, however. A celebrity who often bristles in the media glare, Madonna may be universally admired but she is not universally loved. Her decision in 2006 to adopt a young Malawian boy whose mother died was controversial both in the southern African country and further afield. Madonna has two other children -- son Rocco with her husband British film director Ritchie, and daughter Lourdes from a previous relationship. She directed her first feature film that came out in 2008, and although reviews were mixed, there were harsh words for a woman some feel should forget about movies and stick to music. Her eight-year marriage to Ritchie has come under increasing scrutiny after tabloid newspapers in Britain, where she spends much of her time, have reported that the couple are planning to divorce. Both Ritchie and Madonna have denied the reports. (Agencies)  ... read more »