Effect of postoperative radiotherapy on peripheral blood lymphocytes in patients with carcinoma of the breast

The effect of prophylactic postoperative radiotherapy in patients with carcinoma of the breast was determined on cells in the peripheral blood. Controls had carcinoma of the breast treated by radical mastectomy. Results were also compared with those in patients with carcinoma of the cervix treated by radiotherapy. None had recurrent disease. Radiotherapy of carcinoma of the breast decreased the total white blood cell count by 15% during the period of the first 6 months but did not alter the granulocyte count. The total white cell and granulocyte counts did not change in those with carcinoma of the cervix. The lymphocyte count was decreased by one third for 12 months in patients given radiotherapy for carcinoma of the breast and for 24 months in those with carcinoma of the cervix. The lymphopenia persisted in many for 60 months. Function of the lymphocytes was determined by their ability to synthesize nucleic acids when grown in tissue culture with the strong mitogen phytohemagglutinin (PHA). Radiotherapy produced 50% increase in DNA synthesis for 12 months in patients with carcinoma of the breast and for 60 months in those with carcinoma of the cervix. Treatment had no effect on RNA synthesis in patients with carcinoma of the breast but caused a 25% decrease in RNA synthesis for 60 months in those with carcinoma of the cervix. We are unable to explain the prolonged lymphopenia and the decrease in RNA synthesis. Lymphocytes transformed by PHA are mostly thymic-dependent and responsible for cellular immune response. Since the lymphocyte count was decreased by one third and DNA synthesis increased by a greater amount, the number of thymic dependent lymphocytes did not change or may have increased. The cellular immune response to cancer is unlikely to be impaired by local radiotherapy.