Hello Hema, thank you for your question. I am Dr Asanhanwa Carlson. Non hodgking lymphoma is a form of cancer which affect a certain type of blood cells called lymphocytes and these cells are mainly seen in lymph nodes. This is the reason why patients with this type of cancer would have enlarged lymph nodes. The fact that your father presents with lumps in his thighs two months after he completed chemotherapy could be an early sign of recurrence of his cancer which should be taken very seriously. This is due to the fact that most cancer patients delay and only present to the hospital when their disease is far advanced and little or nothing can be done and secondly a recurrent cancer should be treated as early as possible else the outcomes are generally poor. I would advise you to immediately take your father to his consulting physicians so that appropriate treatment is started as early as possible. To answer your question, I would say YES IT IS SERIOUS. Keywords Recurrence, early consultation, appropriate treatment