For the past six weeks my partner has been suffering from severe pain when standing or sitting. After a MRI found a mass on his lower spine,surgical biopsy performed. Some three weeks later we still dont know what it is, they say they have ruled out cancer and are leaning towards some type of infection. Cultures are being done, but they say they too may no give us the answer. Any clues to what this may be?

To be honest, there are too many possibilities to even make an educated guess. The fact that the mass isn't malignant is a very good sign. Depending on where he's lived, etc, the mass could be TB, histoplasmosis or another fungal infection. I assume that in addition to the biopsy all relevant blood and urine tests have been sent that could shed some light (such as histo comp fix blood test and histo urine antigen). If your partner had recently (within the 2-3 months prior to his symptoms) begun a potent combination of medications for HIV, this could be an "immuje reconstitution syndrome", and may improve on its own with time.