A 27-year-old woman has undergone a sector resection of mammary gland tissue. In the excised tissue, macroscopy detects a dense white node, 4 cm in diameter, with clear boundaries. Urgent histology shows that the tumor consists of a large amount of fibrous stroma with stromal proliferation around the small canaliculi. Canalicular epithelium overlays the basement membrane and retains its polarity. What disease can be characterized by these pathological changes?