blood cell found in the blood of children with acute leukemia. None of the cultures from children with various other disorders or from normal children showed such changes. The factors responsible for these changes are unknown.

Immunologic studies

Observation of virus particles with the electron microscope is only suggestive evidence of the presence of viruses. However, by the use of other methods, such as the immunofluorescent technique, it is possible to obtain additional evidence of the presence of viruses in human leukemic cells and blood plasma and in cultures of cells from patients with leukemia and lymphoma. In the test, antiserum prepared in rabbits against virus-like particles recovered from human leukemic blood plasma is combined with a fluorescent dye. A positive reaction of the antiserum, as indicated by fluorescence, with cells from a test culture, indicates that the cells contain an antigen (“foreign" substance) that may be, but has not yet been proved to be, virus associated. About half of the established cell lines showed such immunofluorescence. The percentage of fluorescent cells in a given culture corresponded approximately to that of cells showing virus particles with the electron microscope.

Dr. Mary A. Fink and her associates of the Institute's Viral Leukemia and Lymphoma Branch found that immunofluorescence of cells from leukemia patients is related to the stage of the disease. Antiserum prepared against human leukemic material in which virus particles were found reacted with the blood cells of approximately 70 percent of patients in the active phases of their disease, and in less than 30 percent of patients in remission. No reaction was observed in specimens from normal persons or patients with other diseases.

Human gamma globulin (the fraction of blood that contains antibodies) was demonstrated for the first time in continuous tissue culture cell lines of human lymphoid cells, including many derived from Burkitt's lymphoma. This finding by Dr. John L. Fahey, Chief of National Cancer Institute's Immunology Branch, suggests the possibility of mass producing in tissue culture the specific antibodies needed for protection against disease.

Chromosome studies

Efforts to understand the nature of leukemia and lymphoma have prompted many studies of the chromosomal constitution of leukemic cells. The chromosomes carry the hereditary factors, or genes, of an individual and are constant in number in every species.

The only consistent chromosomal abnormality ever found in studies of cancer cells has been the Philadelphia chromosome, which is present in a majority of patients with chronic myelogenous leukemia (CML) and is unaffected by treatment. In a recent study by scientists at the National Institute of Arthritis and Metabolic Diseases and National Cancer Institute investigators of the Medicine Branch, patients who lacked the Philadelphia chromosome were found to respond less well to drug treatment and die sooner than those with the abnormality. This difference suggests that CML in patients who lack the Philadelphia chromosome may be a distinct clinical entity.

Dr. Robert W. Miller, Chief of National Cancer Institute's Epidemiology Branch, reported that congenital defects occur together with leukemia more often than can be attributed to chance. Clues to causation may be found in studies of relationships among these conditions.

For example, an excess of congenital defects and leukemia occurred in Hiroshima following the atomic bomb explosion. Environmental agents suspected of causing cancer-radiation, chemicals such as benzene, and viruses-can produce long-lasting genetic abnormalities. In addition, abnormal chromosomes characterize certain genetic disorders associated with a high risk of leukemia. It has been observed that the development of leukemia may be related to chromosomal breakage, whether inherited or acquired, as by exposure to ionizing radiation.

There is strong suggestive evidence that other genetic diseases, which are characterized by immunologic deficiency, such as congenital agamma-globulinemia, carry a high risk of lymphoma. Preliminary clinical and experimental data suggest that “acquired” immunologic deficiency is a precursor of lymphoma. These inter-relationships indicate that chromosomal and immunological abnormalities are probably related to the origin of leukemia and lymphoma, rather than to conditions accompanying these diseases.

TREATMENT OF LEUKEMIA AND LYMPHOMA

The most important recent advance in leukemia therapy has been intensive treatment with combinations of drugs active against the acute leukemias. Many laboratory studies and a few clinical studies to date have indicated that high doses of combinations of drugs administered for short periods, alternately with rest periods, appear to be more effective than other dosage schedules in producing long-term survivals. The goal of such treatment is destruction of all leukemic cells with minimum toxicity to the patient.

In a study reported by Dr. Edward S. Henderson, National Cancer Institute's Medicine Branch, children with acute leukemia were treated with high doses of four anticancer drugs by a 15-month intermittent schedule. The patients were relieved of all symptoms and signs of their disease for initial periods twice as long as those previously reported in studies of combination drug therapy, and they did not become resistant to the drugs. According to recent data, most of the 35 patients achieved complete remission for an average duration of about 13 months. Remission was re-induced in a large percentage of these patients after their disease recurred, and the average total survival time at last report was projected at more than three years.

At

Other investigators are studying the effects of treatment with drugs in combination with radiation, or with total-body radiation. In a study by Dr. Phillip George and his colleagues at St. Jude Children's Research Hospital and the University of Tennessee, combination of five anticancer drugs and a dose of radiation to the patients' central nervous system to destroy “hidden” leukemic cells were administered. At the last report in November 1966, most of the 32 children had achieved complete remission lasting longer than 19 months. that time the median survival time was estimated to be about 28 months. Dr. Ralph E. Johnson, Chief of the National Cancer Institute's Radiation Branch, reported preliminary results of treating small groups of leukemia and lymphoma patients with total-body radiation administered daily in small doses over several weeks. Total-body radiation has been investigated from time to time over many years, but has generally not been given in fractionated doses. A small group of lymphosarcoma patients showed a significant decrease in tumor size following an initial course of radiation and suffered very little illness due to the radiation. One patient at the time of reporting had maintained complete remission for 14 months with monthly exposures of 10 to 20 roentgens (units of radiation delivered).

In another small group of patients with chronic lymphocytic leukemia. Dr. Johnson reported that high lymphocyte counts were markedly decreased following fractionated total-body radiation administered in small doses, and symptoms of the disease were much improved. The results of this study suggested that there may be a qualitative difference between the leukemic and nonleukemic lymphocytes in sensitivity to radiation. This conclusion is based on the finding that in a control group of nonleukemic patients the lymphocyte counts which had not been elevated before radiation were hardly affected by the treatment. Success in treating Hodgkin's disease, a type of lymphoma affecting the lymph glands and other infection-fighting tissues, is one of the most encouraging recent achievements in cancer therapy. Results of studies reported by scientists in several countries show that if the disease is discovered when it is localized and treated with intensive doses of X-ray, it can be completely controlled in nearly half of the patients for 15 years or more. Such patients can be regarded as cured.

Studies by Dr. Henry S. Kaplan at Stanford University and others have shown that the destructive dose for malignant cells in Hodgkin's disease is about 3,500 to 4,000 rads (units of radiation absorbed by tissue). Studies by Dr. Kaplan and others, which have shown that the disease spreads to adjacent lymph nodes in an orderly progression, have led to adoption of procedures for treating nodes in the immediate area of known disease with X-ray to ensure destruction of all malignant cells.

Dr. Johnson reported recently the use of radiation therapy in advanced Hodgkin's disease in which multiple lymph node areas were involved. Using carefully designed treatment schedules, he has administered high doses of radiation to many lymph node areas known to contain the tumor. Complete remissions have been observed in a majority of patients and undesirable side effects of such extensive irradiation have been tolerated satisfactorily.

Many studies are in progress to yield information on the action of chemotherapeutic agents on cells in the hope that a better understanding of the effects of drugs will lead to improved techniques for treating malignant disease. Preliminary studies suggested, for example, that rapidly multiplying mouse lymphoma cells in culture were several times more sensitive to an anticancer drug, -fluorouracil, than the normal bone marrow cells. If the differences in sensitivity to drug action are found to be related to certain stages in the life span of cells, then techniques of administering drugs to patients may be developed to capitalize on the vulnerable periods in the life of leukemic cells.

Other studies are emphasizing improvement in drugs. Cytosine arabinoside represents a new class of compounds of interest because it is active in early clinical studies against the acute leukemias in children and adults. Until now drugs have been relatively ineffective against the type of acute leukemia that occurs in adults, while five drugs have been found useful against acute leukemia in children. Another property of interest to clinicians is that the drug can be given in large doses, which are effective quickly, and then is rapidly eliminated from the body.

VIRAL CAUSATION OF SOLID TUMORS

Research on a possible viral cause of human solid tumors, such as those that occur in the lung, breast, or stomach, has been stimulated by the discovery of numerous virus-induced tumors in animals. In contrast to the leukemia-inducing viruses, which contain RNA (ribonucleic acid), many viruses that cause solid tumors in animals are of the DNA (deoxyridbonucleic acid) type. This difference in type of viral nucleic acid adds a new element to the problem of implicating DNA viruses in the causation of cancer. RNA viruses can be recovered from leukemic blood and tissue, but DNA viruses disappear from the tumor cell and cannot be recovered from tumors. Much of the research effort to date has been devoted to developing techniques for identifying DNA viruses in solid tumors. Laboratory studies have shown that DNA viruses leave behind the information for the cell to synthesize a distinctive antigen, or "foreign" substance, that appears in the tumor cell after virus infection. Such antigens have been designated "T" (for tumor) antigens, and can be detected by their reaction with specific antibodies found in the blood serum of the host. Recent research has revealed the presence of "T" antigens in cells of tumors in hamsters and other rodents induced by human adenoviruses, which cause respiratory disease. Another DNA virus detected by its "T" antigen is SV40, which was isolated from tissues of the Indian monkey in which it apparently does no harm, but induces tumors in young hamsters.

Means of detecting antigens left behind by viruses may lead to the discovery of human cancer-causing viruses. Large-scale studies are in progress to examine blood serums of large numbers of cancer patients and normal controls for the presence of antibodies to DNA viruses.

Another clue to the presence of DNA viruses has come from the discovery that they may combine with other viruses to form hybrids. For example, a virus was discovered that appeared to be a hybrid between a human virus, adenovirus type 7, and SV40, present as a passenger in monkey kidney cells in which the adenovirus was being grown for vaccine production. The hybrid virus, which caused tumors in newborn hamsters, was believed to consist of a core of SV40 nucleic acid, alone or in combination with adenovirus 7 nucleic acid, wrapped in the protective protein coat of the adenovirus.

The concept of virus partnerships has implications for human cancer in addition to its possible usefulness in detecting DNA viruses. If hybridization of viruses is found to be a general phenomenon, it might suggest ways in which a relatively harmless virus could conceivably combine with another virus to become a highly malignant one.

A study by Dr. Alan Rabson and his associates in the National Cancer Institute's Pathologic Anatomy Branch has suggested that SV40 can form a hybrid with herpes simplex virus (a cause of cold sores). When monkey kidney cells growing in culture were inoculated with SV40 and about 24 hours later with herpes simplex virus, 5 percent of the cells contained both viruses within the same nucleus.

It is believed that DNA viruses may integrate their genetic material with that of the host cell and direct the cell to produce new viral materials. Results of a study reported in the past year showed that the RNA produced in adenovirus

infected human cancer cells in culture consisted of an increasing amount of viral messenger RNA and a constant fraction of host cell messenger RNA. (Messenger RNA carries genetic information from one part of the cell to another where it acts as a template for formation of proteins.) These results also indicated that the infected host cell continued to produce its own RNA. The study was conducted by Dr. James A. Rose, National Institute of Allergy and Infectious Diseases, and scientists of the Metabolism Branch of the National Cancer Institute. Another phenomenon showing the effect of combination of viruses is represented by the "helper" action of a mouse leukemia virus in completing a defective solid tumor-inducing RNA virus to form a fully infectious particle. Dr. Robert J. Huebner, National Institute of Allergy and Infectious Diseases, recently reported results of such a study. A mouse virus that induced solid tumors (sarcomas) in newborn hamsters could not be detected in the tumor tissue or recovered from it. Furthermore, extracts of the tumors did not cause new tumors when inoculated into newborn hamsters and did not induce foci of infection in tissue cultures. This indicated that infectious virus was absent from the extracts. However, when the hamster tumor cells were grown with mouse embryo cells and the mixed culture inoculated with mouse leukemia virus, focus-forming and tumor-inducing viruses were readily recovered. Preliminary studies indicated that the focus-forming viruses thus recovered had the outer-coat antigens of the "helper" virus and thus represented a newly created type of the sarcoma virus. In the development of the breast tumor of mice, a well known animal cancer, three factors are involved: cancer-causing virus (the mammary tumor agent), genetic susceptibility, and hormonal stimulation. Dr. Vernon Riley at SloanKettering Institute for Cancer Research showed that infection with LDH virus is a protective factor. LDH virus is widely distributed in mouse colonies but does not cause any known disease. It can be identified by the fact that it increases the activity of lactate dehydrogenase and other enzymes in the blood plasma. Mice infected with LDH virus had a significantly lower incidence of breast cancer, and developed such tumors later, than control mice not infected with the virus.

Research on DNA viruses is a rapidly expanding program of the National Cancer Institute. An important segment of the research is conducted by the National Institute of Allergy and Infectious Diseases. Other key studies are being carried out at research institutions and medical schools in this country and abroad, all aimed ultimately at evaluating the role of DNA viruses in the causation of human cancer.

TREATING SOLID TUMORS

A number of studies reported in the past year showed encouraging progress in the treatment of tumors in children. Dr. Sidney Farber, Director of Research, Children's Cancer Research Foundation, Boston, reviewed the results of longterm studies of treatment of Wilms' tumor, a cancer of the kidney in children, using a combination of an antibiotic, actinomycin D, surgery, and radiation. Almost all of a group of 53 children without widespread disease survived at least two years (in this disease almost always equivalent to cure) and some at the time of reporting had survived almost 10 years. Of 31 children whose disease had already spread to the lungs, an apparent cure rate of nearly 60 percent was achieved. Similar findings were reported in a group of 34 patients studied by Dr. Dale G. Johnson and his colleagues at the Children's Hospital of Philadelphia. Both groups have concluded that Wilms' tumor treated by surgery, radiation, and actinomycin D should be cured in most instances.

Dr. Wataru W. Sutow and his associates at the M.D. Anderson Hospital and Tumor Institute, Houston, Texas, reported that about one-third of a small group of children with cancers of the soft tissues, most cancer of the muscle cells, responded temporarily to therapy with vincristine, a drug derived from the periwinkle plant. One child was free of tumor two years after conclusion of the therapy.

To treat a variety of solid childhood tumors, concurrent chemotherapy with vincristine and actinomycin D was used by Dr. David H. James and his associates of St. Jude Children's Research Hospital and the University of Tennessee. Almost all of a group of 18 children with inoperable tumors showed some response lasting from 1 to 28 months. In two children, radiation following response to chemotherapy brought about further tumor regression, making surgery possible. The two drugs were used without severe toxicity, and with a possible additive antitumor effect.

Retinoblastoma, a malignant tumor of the eye, usually is found in children under the age of four, and one-third of the cases involve both eyes. It occurs once in approximately 23,000 births and is considered to be a congenital tumor. The aim of treatment is to save not only the life of the child, but also vision in at least one eye.

Dr. George A. Hyman and his associates at the Columbia University College of Physicians and Surgeons reported on 250 children with retinoblastoma affecting both eyes and with an outlook ranging from very favorable to very unfavorable. After treatment with a drug, triethylene melamine (TEM) prior to and following radiotherapy, the children had responses ranging from "useful vision and cure rate" of 85 to 22 percent. In another report by Drs. Algernon B. Reese and Robert M. Ellsworth of the same hospital, the dramatic effect of TEM on retinoblastoma was confirmed. These investigators suggested the occurrence of an additive effect in the action of combination radiation and drug therapy.

Reports on solid tumors affecting adults included an evaluation of treatment of a relatively rare type, cancer of the adrenal gland, first reported responsive to a drug, ortho,para' DDD, by the late Dr. Delbert M. Bergenstal and his associates of the National Cancer Institute. The drug, called o,p' DDD for short, whose production was sponsored by the Institute, is related to the insecticide DDT. Results of treatment with o,p' DDD evaluated by Drs. Adolph M. Hutter1 and Donald E. Kayhoe of the Institute's Chemotherapy Area, indicated that more than one-third of a group of 59 patients with evaluable, measurable disease had objective remission of their cancer lasting an average of about seven months after treatment.

Treatment of inoperable lung cancer with a combination of radiation and a drug, 5-FU (5-fluorouracil), was reported by Dr. Fred J. Ansfield and his associates at the University Hospitals, Madison, Wisconsin. A small group of 13 patients so treated had an average survival of almost two years at the time of reporting, and three were living more than five years. A similar group of 13 patients receiving radiation alone had an average survival of six months; one patient survived 14 months.

In another study, a small group of patients with far advanced reticulum cell sarcoma, related to the lymphomas and arising most frequently in lymph nodes, improved dramatically when given small doses of vincristine over a long period, despite the fact that these patients were previously resistant to other forms of therapy. Dr. William J. Yount and his associates at the United States Public Health Service Hospital, Boston, reported that signs of the tumors completely disappeared in 3 out of 9 patients, and regression was almost complete in 3 others. Remissions in these patients lasted 3 to 17 months.

Recent results show that some forms of cancer of the testis, often unresponsive to surgery and radiation treatment, are responsive to drugs. Dr. David A. Karnofsky reported that among 150 patients with advanced testicular cancer treated at the Memorial Sloan-Kettering Cancer Center, New York, with a combination of three well known drugs-actinomycin D, methotrexate, and chlorambucil-11 achieved long remissions. Nearly half of these patients survived free of disease longer than 10 years.

SMOKING AND LUNG CANCER

The problem of smoking as the principal cause of lung cancer continues to be a major source of concern to the National Cancer Institute. In the past year, several large statistical studies added new data to the evidence of the smoking and lung cancer relationship. In one, results were published on a study of 250,000 white male United States veterans that was begun in 1954 by the National Cancer Institute in cooperation with the Veterans Administration. The findings showed that cigarette smokers had a higher death rate than nonsmokers for lung cancer and almost every other disease. In one age group, 11 times as many smokers as nonsmokers died of lung cancer, and 12 times as many died of emphysema, also a lung disease.

Studies have shown that, among lung cancer patients, women have a survival advantage over men. Survival rates are lower among all patients with epidermoid carcinoma, the most common type of lung cancer in men, than among patients with adenocarcinomas, which occur more frequently in women. Dr. Roger R. Connelly and his associates of the National Cancer Institute's Biometry Branch

1 Now of the University of Rochester School of Medicine. Rochester, New York.

2 Now of the National Institute of Allergy and Infectious Diseases.