Lymphoma of the thymus is a type of cancer that affects the thymus gland, which is located in the chest. It is characterized by the abnormal growth of lymphocytes, a type of white blood cell. This type of lymphoma is typically more common in males rather than females, making the statement "More common in females" false. Lymphoma of the thymus is known to be slow-growing, meaning it progresses at a relatively slow rate. It can often be confused with undifferentiated tumors, as the symptoms and presentation may be similar. Additionally, it may present with respiratory distress and dysphagia, which are symptoms caused by the tumor's location in the chest. Therefore, the statement "Slow growing" is the correct answer.