What is inside the cysts of fibrocystic breast disease?

Endocrine System Case Study
Joan Barker, age fifty-six years, comes for a routine physical examination. She states that she has been in perfect health and has no complaints. She has a history of asthma but currently requires no medications of any kind. Her physical examination is completely normal, except for a 2-cm firm, nontender, nonmobile mass in the upper outer quadrant of her left breast. She indicates that she does not perform regular breast self-examination and that she did not know the mass was there. She has no family history of breast cancer and has never been pregnant.
Answer the following questions about Ms. Barker’s condition:
• What term is used to describe the benign condition that may have caused Ms. Barker’s breast mass?
• What is inside the cysts of fibrocystic breast disease?
• Mammography and ultrasonography reveal a solid lesion (not cystic). What is the most common type of breast cancer?
• Biopsy determines that Ms. Barker has invasive carcinoma of the breast. What is the difference between ductal carcinoma in situ and invasive carcinoma of the breast?
• Ms. Barker’s breast cancer has metastasized to her lungs. What is the difference between metastatic lung cancer and primary lung cancer?