Hard lumps on the chest of men may be in the developmental stage, or it may be related to gynecomastia, breast cancer, and so on. 1. In the developmental stage: If a man is in the developmental stage, the estrogen in his body will be relatively high, which will make his chest develop, and there will be hard lumps on his chest. With the growth of age, the content of androgen in the body will slowly increase, and the situation of hard lumps in the chest will slowly improve. 2. Gynecomastia: Gynecomastia is a disease in which the ratio of estrogen and androgen in the male body is imbalanced due to various reasons, which leads to abnormal growth and development of breast tissue. Gynecomastia may lead to hard lumps inside the chest, and may also show unilateral or bilateral breast enlargement. 3. Breast Cancer: Breast cancer in men can also lead to lumps in the breasts. However, the chance of men developing breast cancer is relatively low, accounting for 1% of breast cancer patients. In addition, you should also consider mastitis, fibroid and other benign diseases, as well as chest wall diseases, you can go to the hospital to find out the cause.