The surgical specimen is sent fresh from the surgical suite to the laboratory for frozen section examination. Before cutting into the specimen, the pathologist makes a careful gross examination, which demonstrates that most of the specimen has replacement of the normally fatty breast tissue with strands of dense, white, firm tissue. In a few areas, roughly spherical lesions up to 3-cm diameter with a bluish hue to them are seen. Palpation of these areas produces a fluctuant sensation. Which of the following is the MOST likely diagnosis based on the gross evaluation?