A. Introduction and Presentation of Data.- 1. Criteria for Diagnosis.- 2. Classification.- 3. Selection of Cases for Our Study.- 4. Observations.- 5. Rate of Occurrence.- 6. Report of Cases.- Summary.- References.- B. Multiple Primary Malignant Neoplasms of Different Tissues or Organs.- 1. Introductory Comments.- Reference.- 2. Occurrence of Multiple Cancers within the Same or Related Organ Systems.- a) Multiple Cancers Involving the Female Genitalia and Breasts.- b) Coexistence of Epithelial Carcinoma of the Bladder and Adenocarcinoma of the Prostate.- References.- 3. Second Primary Cancers Induced by Treatment of an Initial Malignant Neoplasm.- a) Therapeutic Ionizing Radiation.- b) The Stewart-Treves Syndrome.- c) Carcinoma of the Male Breast Developing during Estrogen Therapy for Carcinoma of the Prostate.- References.- 4. Hereditary Influences in Patients with Multiple Primary Malignant Neoplasms.- References.- 5. Blood Groups and Multiple Primary Malignant Neoplasms.- References.- 6. Leukemia or Lymphoma and Coexistent Primary Malignant Neoplasms.- a) Cases Reported in the Literature.- b) Selection of Our Cases for Study.- c) Leukemia Plus Malignant Lesions.- d) Lymphoma Plus another Malignant Lesion.- e) Coexistence of Kaposi’s Sarcoma and Leukemia or Lymphoma.- f) Coexistence of Epitheliomas of the Skin and Chronic Lymphatic Leukemia.- g) Cancer and Acute Leukemias: Effects of Radiation.- h) Incidence.- i) Comment.- Summary.- References.- 7. Carcinoid Tumors of the Small Intestine and Second Primary Cancers.- References.- 8. The Coexistence of Primary Lung Cancer and Other Primary Malignant Neoplasms.- a) Selection of Cases.- b) Observations.- c) Comment.- Summary.- References.- C. Multiple Primary Malignant Neoplasms of Multicentric Origin.- 1. Introductory Comments.- References.- 2. Multicentric Epitheliomas of the Skin.- References.- 3. Multicentric Carcinomas of the Oral Cavity.- a) Selection of Cases.- b) Observations.- c) Comment.- Summary.- References.- 4. Multicentric Epitheliomas of the Lips.- References.- 5. Multicentric Epitheliomas Involving the Larynx, Pharynx, and Esophagus.- Reference.- 6. Multicentric Adenocarcinomas of the Stomach.- a) Present Study.- b) Results.- c) Comment.- References.- 7. Multicentric Carcinoid Tumors.- References.- 8. Multicentric Adenocarcinomas of the Colon and Rectum.- a) Selection of Cases.- b) Results.- c) Comment.- Summary.- References.- 9. Multicentric Epitheliomas of the Urinary Tract.- a) Multicentric Tumors of the Bladder.- b) Multicentric Lesions Associated with Neoplasms of the Renal Pelvis.- References.- 10. Multicentric Carcinomas of the Cervix, Vagina, Vulva, and Anus.- Reference.- 11. Bilateral Carcinomas of the Breast.- a) Criteria for the Diagnosis of Independent Cancer in the Second Breast.- b) Observations.- c) Unsimultaneous (Nonsynchronous) Cancer in the Second Breast.- d) Simultaneous (Synchronous) Cancer in the Second Breast.- e) Independent Cancers of the Second Breast in Association with Other Primary Malignant Neoplasms.- f) Comment.- g) The Problem of Prophylactic Simple Mastectomy of the Second Breast.- Summary.- References.- 12. Bilateral Testicular Cancers.- References.- 13. Bilateral Ovarian Carcinomas.- References.- 14. Multicentric Bronchial Carcinomas.- References.- 15. Multicentric Carcinomas of Parenchymatous Organs.- a) Multicentric Carcinomas of the Kidney.- b) Multicentric Carcinomas of the Thyroid and Pancreas.- c) Multicentric Hepatomas.- Reference.- 16. Multicentric Gliomas of the Central Nervous System.- References.- 17. Multicentric Malignant Neoplasms of the Reticuloendothelial System.- Reference.- 18. The Case for Multicentricity of Origin of Malignant Neoplasms.- References.- Summary.