Final answer:
The diagnosis for well-circumscribed lumps in the breast associated with menses is fibrocystic changes, which is due to hormonal fluctuations during the menstrual cycle leading to the formation of fluid-filled cysts and fibrotic areas in the breast tissue.
Step-by-step explanation:
The most likely diagnosis for multiple round, well-circumscribed fluctuant and firm, mobile lumps in the breast that are associated with the menstrual cycle is D) Fibrocystic changes. This condition is influenced by the hormonal fluctuations that occur during the menstrual cycle. The estrogens and progesterone can cause the breast tissue to swell and become tender, especially during the secretory phase. In fibrocystic changes, the breast may develop fluid-filled cysts and areas of fibrosis, which present as lumps that may vary in size and feel throughout the menstrual cycle. Unlike fibroadenomas which are usually singular, non-cancerous growths, or breast abscess and mastitis, which are characterized by infection and inflammation, fibrocystic changes often do not require treatment unless symptoms are severe. Monitoring is important, and carrying out a monthly breast self-exam is advised to check for any abnormal changes.