Which of the following helps in differentiation of follicular carcinoma from follicular adenoma of thyroid

Ref Robbins 9/e p1094 Microscopically most follicular carcinomas are composed of uniform cells forming small follicles.follicular carcinomas may be grossly infiltrative or minimally invasive. The latter are sharply demarcated lesions on gross examination . This distinction requires extensive histologic sampling to exclude capsular or vascular invasion