What are possible reasons for small sore lump just beside left nipple of 35 year old male?

A small sore lump beside the left nipple in a 35-year-old male could be due to several reasons, including gynecomastia (enlargement of breast tissue), a cyst, or an infection such as mastitis. It may also be related to hormonal changes, trauma, or even a benign tumor. However, it is essential to consult a healthcare professional for an accurate diagnosis and appropriate treatment.