Suspected to have a lung cancer fine needle biopsy found a few atypical cells and no malignant cells?

I am sending this question for my mother in law who has been suffering from cough for about 2 months. She was suspected to have a lung cancer since the CT scan reveals several nodules on her lungs. She was tested for sputum and came out negative. She also underwent fine needle biopsy but it did not rule our the carcinoma even though they only found a few atypical cells and no malignant cells are found. What other tests can we do to confirm or totally rule out the possibility of having a cancer? Aside from lung cancer, what are the other possible illness that has these same symptoms? Does the attached biopsy insufficient to rule our carcinoma? She is 57 years old.