NEW YORK ( TheStreet) -- Radian Shares ( RDN) fell sharply after the company became the latest mortgage insurer to announce capital-raising plans. Radian Group said late Monday it will offer up to $550 million of common stock, and that underwriters will have the option to purchase up to an additional 15%, or $82.5 million, to cover overallotments. Net proceeds from the offering may be used for additional capital support for its mortgage insurance business and repurchases of, or payments on, its outstanding debt securities, Radian said. The stock offering announcement came as Radian Group reported a first-quarter loss of $3.77 a share, which grew from a year-ago loss of $2.69 a share. Mortgage insurance provision for losses rose 64%, the company said. Last month, both MGIC Investment ( MTG) and The PMI Group ( PMI) announced stock offerings after posting quarterly losses. Radian Group shares were plummeting, down $1.61, or 11%, to $13.02. Volume totaled 1.74 million shares, compared to the three-month average daily volume 4.72 million. Elsewhere, PhotoMedex ( PHMD) priced an offering of 500,000 shares of common stock at $6 per share. Underwriters were granted a 45-day option to purchase an additional 75,000 shares to cover overallotments. Shares were sliding on the announcement, falling 7.6% to $6.10. Pennsylvania Real Estate Investment Trust ( PEI) also lost ground on news of a stock offering. The company priced a 9 million common stock offering at $16.25 a share. Underwriters were granted a 30-day option to purchase an additional 1.35 million shares to cover overallotments. Net proceeds from the offering will be used to repay borrowings under the company's 2010 credit facility. Pennsylvania REIT shares were off 5.9% to $16.33. Volume of 2.46 million shares was easily outpacing the three-month average daily volume of 537,000. In a shelf registration with the Securities and Exchange Commission, Arena Pharmaceuticals ( ARNA) said it may offer up to $150 million in mixed securities from time to time. Shares of Arena were down 2.4% to $3.23. Oxygen Biotherapeutics ( OXBT) dropped 15.7% to $4.08 after the company said it will sell 1.72 million shares of common stock and warrants to purchase an additional 732,758 to certain institutional investors. The common shares and warrants are being offered in units, which consist of one common share and a warrant to purchase 0.425 share of common stock at a price of $2.90 per unit. The warrants have a term of five years and an exercise price of $5.32 per share.