Could it happen such that a benign thyroid nodule turn into malignant years later?

Not likely: Benign thyroid nodules almost always remain that way. The more likely instance is that a malignant nodule grew within the benign nodule (more likely when the benign nodule is large). These are usually examined on ultrasound and biopsies via fine needle aspiration or core biopsy. Read more about it here: http://www.Conciergeradiologist.Com/ultrasound-guided-biopsy.Html.