A 28-year-old woman presents with amenorrhea, galactorrhea, and infertility. Serum prolactin is markedly elevated. MRI shows a 0.8 cm sellar mass. Histopathology of the lesion shows monomorphic cells arranged in nests and trabeculae. The structure marked **B** in the diagram demonstrates loss of the normal reticulin framework seen in adjacent pituitary tissue. Which of the following best explains the histological significance of this finding in pituitary adenomas?