UPDATE 2-Cigna tops profit estimates, raises 2017 profit forecast

(Adds forecast, background on Obamacare)

Nov 2 (Reuters) - Cigna Corp reported a better-than-expected quarterly profit, helped by higher enrollments and lower costs in its commercial business, and joined larger rivals in raising its full-year earnings forecast.

The results come at a time when the health insurance sector is facing uncertainties around former President Barack Obama's healthcare law.

Cigna is one of the few remaining insurers offering Obamacare health plans even as major health insurers have either scaled back or pulled out of the market.

Evercore ISI analyst Michael Newshel said Cigna continued the string of strong beat and raises from health insurers on lower-than-expected medical costs.

Cigna's membership rose about 4 percent to 15.8 million as of Sept. 30, while its commercial medical loss ratio came in at 78.6 percent in the quarter compared with 79.4 percent, a year earlier.

Medical loss ratio - a key performance metric for the sector - is the amount an insurer spends on medical claims compared with income from premiums.

Cigna said it expects 2017 adjusted income from operation to $10.20 to $10.40 per share, up from its previous estimate of $9.75 to $10.05.

The company's net income rose to $560 million, or $2.21 per share, in the third quarter ended Sept. 30, from $456 million, or $1.76 per share, a year earlier.

Excluding items, the company earned $2.83 per share, above the average analyst estimate of $2.36, according to Thomson Reuters I/B/E/S.

Total revenue increased 5 percent to $10.4 billion. (Reporting by Ankur Banerjee in Bengaluru; Editing by Saumyadeb Chakrabarty)