Dina Lohan's Still Hospitalized ... Family Fears It's Cancer

Dina Lohan's family is afraid she might have cancer ... as doctors remained baffled about the cause of her stomach pain after more than a month in the hospital.

According to our Lohan fam sources, Lindsay's mama has undergone a battery of tests -- at 2 different hospitals -- since she was admitted for treatment last month. We're told she had a biopsy on a nodule found in her throat. She's currently waiting for the results.

Doctors gave her a round of antibiotics ... believing her pain was caused by a dental procedure gone wrong, but that only worked for a short time before the pain returned.