(ShareCast News) - Shares in women's value retailer Bonmarche tumbled as the company warned over its full year profits and said chief executive Beth Butterwick was stepping down.The group had said in its interim results in November that its expectations for the year would remain unchanged provided trading conditions normalised for the remainder of the financial year.However, Bonmarche said on Wednesday that conditions this month, particularly since 'Black Friday' at the end of November, have been very challenging and have not normalised."The board's view is that these trading conditions are likely to continue for the remainder of the winter season and it has therefore revised its profit expectations for the current financial year."Given the ongoing volatility of trading conditions, it now expects pre-tax profit to be in the range of £10.5m to £12m.The company also announced that chief executive Beth Butterwick will step down after four years in the role to join Karen Millen.She will remain with the group until her successor is appointed to ensure a smooth transition.At 1020 GMT, Bonmarche shares were down 30% to 209p.