The rate of division of antibody-forming cells during the early primary immune response.

Mitotic blocking agents, colchicine or Velban, were used to estimate cycle times of spleen cells which release hemolysin for sheep erythrocytes (plaque-forming cells). The cells were obtained either from rats immunized with sheep erythrocytes or from cultures of mouse spleen cells immunized in vitro with the same antigen. 2, 3, or 4 days after immunization, animals or cell cultures were treated with mitotic blocking agents for periods of time ranging from 2.5 to 7 hr; plaque-forming cells were then enumerated. Decreased numbers of plaque-forming cells were found after such treatment. The extent of reduction was a function of duration of the drug treatment and the method of immunization, but was independent of the time after immunization. The evidence presented is consistent with premises that: (a) plaque-forming cells in mitosis do not release sufficient antibody to be detected, (b) mitotic blocking agents, by arresting plaque-forming cells in metaphase, prevent not only detection of these cells but also the increase in number of plaque-forming cells which would have resulted from cell division, (c) mitotic blocking agents do not affect release of antibody by cells in interphase. Cell cycle times, based on the extent of reduction of plaque-forming cells per unit time of drug treatment, were estimated using a mathematical model appropriate for an exponentially increasing population of cells. Cell cycle times estimated using the mitotic blocking agents agreed well with cell doubling times calculated from the increase in plaque-forming cells occurring 1-4 days after immunization. Increased responses produced by higher antigen doses or treatment of immunized animals with an adjuvant resulted from an increased rate of division of responding cells and their progeny. The results are consistent with a cell selection theory of antibody formation. Antigenic stimulation causes relatively few cells to proliferate and to synthesize antibody; apparently the magnitude of the response is dependent primarily on the rate of division of responding cells. It is suggested on the basis of observations of in vitro-immunized cell cultures that the rate of division of responding cells may be dependent on the rate of interaction between two cell types, both of which are essential for the in vitro plaque-forming cell response.

Dissociation of antitumor potency from anthracycline cardiotoxicity in a doxorubicin analog.

The search for new congeners of the leading anticancer drug doxorubicin has led to an analog that is approximately 1000 times more potent, noncardiotoxic at therapeutic dose levels, and non-cross-resistant with doxorubicin. The new anthracycline, 3'-deamino-3'-(3-cyano-4-morpholinyl)doxorubicin (MRA-CN), is produced by incorporation of the 3' amino group of doxorubicin in a new cyanomorpholinyl ring. The marked increase in potency was observed against human ovarian and breast carcinomas in vitro; it was not accompanied by an increase in cardiotoxicity in fetal mouse heart cultures. Doxorubicin and MRA-CN both produced typical cardiac ultrastructural and biochemical changes, but at equimolar concentrations. In addition, MRA-CN was not cross-resistant with doxorubicin in a variant of the human sarcoma cell line MES-SA selected for resistance to doxorubicin. Thus antitumor efficacy was dissociated from both cardiotoxicity and cross-resistance by this modification of anthracycline structure.

Noncancer deaths in white adult cancer patients.

BACKGROUND: The cancer-specific death rate is a commonly used indicator in the assessment of progress against cancer. However, since the cause of death is often not substantiated and complete medical information is lacking, the validity of cancer-specific mortality rates is being questioned. PURPOSE: We investigated the validity of the cancer-specific death rate by examining noncancer deaths of cancer patients in a large patient population. METHODS: Data were obtained from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program on cancer patients diagnosed between 1973 and 1987, with follow-up complete through December 1987. The SEER database consists of 1.2 million records from nine population-based registries covering nine geographic regions of the United States. Rates of noncancer deaths in the U.S. population were obtained from the National Center for Health Statistics. Cancer mortality rates were subtracted from overall mortality rates to obtain noncancer death rates by sex and the 5-year age group for each calendar year. Excluded from the study were patients of races other than White and those diagnosed at age 85 years or more due to absence of noncancer death rate comparisons. Also excluded were cancer cases discovered at autopsy and in persons less than 20 years of age. The statistical analysis employed a log-linear model. RESULTS: The ratio of patient-to-general-population noncancer death rates, as calculated by dividing the number of patient noncancer deaths per year by the number found in the matched U.S. population data and referred to as the noncancer relative hazard, is considered significant with values greater than 1 for those with all cancers combined and for the common solid tumors examined. Of the 12 leading causes of death other than cancer in the patient population, the most common causes were circulatory and respiratory failures. The noncancer relative risk of death decreased rapidly after diagnosis and also decreased with the patient's age at diagnosis. It increased slightly with the calendar year of diagnosis. CONCLUSIONS: Because more noncancer deaths occurred shortly after diagnosis, it appears that this excess was caused by treatment of the cancer. Generally, cancer-specific death rates underestimate the mortality associated with a diagnosis of cancer. Therefore, because the degree of underestimation changes with time, an examination solely of cancer-caused mortality in assessing progress against the disease is incomplete.

Assessing changes in the impact of cancer on population survival without considering cause of death.

BACKGROUND: We have previously argued against the calculation of cancer-specific death rates as philosophically undefined and biased. Deaths attributed to cancer during a particular year occur in patients diagnosed during an unknown distribution of past times, so cancer-specific death rates cannot be used to assess changes in the impact of cancer on survival of the population at specific periods of diagnosis. PURPOSE: Our goal was to develop and analyze three measures of the impact of cancer on population survival that do not use the attributed cause of death: 1) the age-adjusted proportion of the population diagnosed with cancer in a particular year and projected to be dead of any cause by a particular age; 2) the same measure corrected for population mortality; and 3) the expected years of life lost to a 20-year-old individual because of the possibility of a diagnosis of cancer. METHODS: Data on all adults diagnosed with any cancer during the period from January 1973 through December 1990 were obtained from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute. The measures were calculated separately for various combined sex and race groups. Three 2-year diagnosis periods spaced 5 years apart were considered: 1975-1976, 1980-1981, and 1985-1986. A statistical model was used to extrapolate survival beyond observation; the same model was used for patients diagnosed in the three time periods to minimize the effect of possible model misspecification on changes. RESULTS: Cancer incidence increased for three of the four sex-race groups; age-adjusted changes from 1975 through 1976 to 1985 through 1986 were +11.5% for white men, +6.9% for white women, +15.1% for black men, and -9.2% for black women. Human immunodeficiency virus (HIV)-related cancers were responsible for an increased cancer incidence at early ages in white men in the latest time period studied. There was a decrease in the incidence of gynecologic cancers at early ages; the decrease was greater among black women (-55.1%) than among white women (-39.3%). Age- and incidence-adjusted 5-year survival increased by 17.9% for white men, 2.3% for white women, and 7.4% for black men and decreased by 14.1% for black women. When the data from 1985 through 1986 were compared with those from 1975 through 1976, the expected number of years lost to a 20-year-old individual because of cancer changed as follows for the various sex-race groups: +1.4% for white men (-4.0% if HIV-related cancers were not included in the calculation), +2.1% for white women, +12.2% for black men, and +8.8% for black women. CONCLUSIONS: For white men and women, there has been an increase in both the incidence of and survival following the diagnosis of cancer; the two effects nearly cancel in our measures. The experience of black men and women has worsened because of increasing incidence or decreased survival.

Tumor volume, nodal status, and metastasis in breast cancer in women.

The relationship between primary tumor volume at detection, number of positive nodes, and probability of and time until first distant metastasis was examined for a group of 2,663 women with breast cancer. Time until metastasis was shown to decrease and probability of metastasis to increase as tumor volume and number of nodes increased. Either factor remained significant after correction for the other. Simple proportional hazards models were shown to be inadequate to describe the data. Graphic techniques were used to obtain nonparametric estimates of the forms of the relationships between tumor volume, nodal status, and the time course of the occurrence of metastasis. A simple calculation demonstrated that the average contribution per cell to the probability of metastasis decreased with increasing volume.

Lack of concordance of growth rates of primary and recurrent breast cancer.

The degree of concordance of growth rates of primary tumors with corresponding recurrences was investigated by using data from 184 patients with breast cancer with measurable recurrences. For conduction of this examination, the detection processes of both the primary tumor and the recurrence were explored. The probability of detection of a recurrence per unit time was found to be nearly proportional to the tumor's diameter. Approximately 60,000 cells initiated the recurrence, and the distribution of doubling times of the recurrences was exponential, with a mean of 2.1 months. The probability of detection of the primary tumor per unit time was approximately proportional to its volume. The distribution of doubling times of primary tumors was nearly exponential; from other evidence, we inferred that the mean doubling time was also close to 2.1 months. Several techniques to measure growth rate agreement between the primary and recurrent tumors within individuals were developed, and all of them yielded the result that the growth rates are nearly unrelated.

Estimation of human tumor growth rate from distribution of tumor size at detection.

Methods are presented for estimating the growth curve of a tumor (up to an unknown scale factor of time) from the distribution of volumes at detection on the basis of two assumptions: 1) the existence of a common growth curve and 2) the assumption that the probability of detecting a tumor in a period of time is proportional to the tumor volume. These methods can accommodate variation between individuals in speed of traversal of the growth curve. The methods are applied to volumes of tumor at detection of a large series of breast cancers. The simplest, adequate description is exponential growth with great individual-to-individual variation in tumor doubling time. The data are consistent with bounded growth (Gompertzian or logistic form) as well as exponential growth. However, there is no evidence that the bound on growth is within the range of the data. The shape of the distribution of volumes does not yield an effective lower limit on such a bound.

Association of levels of circulating C1q binding macromolecules with induction chemotherapy response in head and neck cancer patients.

Ninety-five untreated patients with squamous cell carcinoma of the upper aerodigestive tract expressed significantly higher levels of C1q-binding macromolecules as compared to 45 noncancer-bearing controls. No relationship between C1q-binding macromolecules and levels of circulating IgG-immune complexes as determined by the solid-phase C1q-binding assay or the C3d-solid-phase assay could be defined suggesting that C1q-binding macromolecules were distinct from IgG-circulating immune complexes. An elevated level of C1q-binding macromolecules within these patients was predictive of subsequent response to induction chemotherapy; those with elevated levels characteristically showed no response. Using multivariate logistic regression analysis including the covariates of American Joint Committee staging parameters as well as C1q assay results, levels of the isolated macromolecules added significant prognostic information as to the probability of chemotherapeutic response. The quantitation of C1q macromolecules has clinical implication as to choice of therapeutic regimens against head and neck cancer. The nature of these substances remains to be defined.

Significance of C1q-binding macromolecules within the head and neck cancer patient.

Elevated levels of macromolecules, within the peripheral blood of head and neck cancer patients, capable of binding the first component of complement (C1qBM) in vitro have prognostic implication. Namely, elevated levels of C1qBM have been associated with nonresponse to induction chemotherapy. In this investigation, a series of in vitro studies regarding the biological properties of C1qBM were combined with a longitudinal analysis of 112 previously untreated head and neck cancer patients. Our purpose was to shed light on the biological significance of this circulating macromolecule, a substance composed, in part, of IgG and IgM. A potential confounding influence of C1qBM with induction chemotherapy, which could contribute to observed prognostic findings, was negated by two in vitro observations: the macromolecule failed both to bind the chemotherapeutic agents cisplatin, bleomycin, and 5-fluorouracil and to impede the cytotoxic effect of these same drugs on a cultured human head and neck cancer cell line. The clinical relevance of C1qBM was reinforced by the observation that elevated levels predicted a high probability of death with disease (P = 0.005 by Cox's proportional hazards model). The prognostic implication was independent of the use of induction chemotherapy, i.e., patients with high C1qBM levels treated with multimodality therapy not composed of anticancer drugs did equally poorly. Thus, the prognostic significance of C1qBM in patients undergoing induction chemotherapy appears independent of drug effect and appears reflective of tumors that are more rapidly progressive and potentially less responsive to therapeutic intervention, including combinations of surgery, radiation, and/or chemotherapy.

Cardiotoxicity of epirubicin and doxorubicin: assessment by endomyocardial biopsy.

Forty-two evaluable endomyocardial biopsies were obtained from 29 patients treated with epirubicin, the 4'-epimer of doxorubicin in cumulative doses ranging from 147 mg/m2 to 888 mg/m2. In this study of the Northern California Oncology Group, myofibrillar loss and sarcoplasmic vacuolization were identified and shown to be identical to those previously described for doxorubicin. However, when these biopsies were compared to 119 biopsies obtained from 98 patients treated with doxorubicin, milligram for milligram, epirubicin caused less endomyocardial injury than doxorubicin (P = 0.0013). Age, sex, type of primary malignancy, prior cardiac disease, and hypertension did not influence the degree of histologically demonstrated anthracycline injury induced by epirubicin.

Impact of prophylactic immediate posttransplant ganciclovir on development of transplant atherosclerosis: a post hoc analysis of a randomized, placebo-controlled study.

BACKGROUND: Coronary artery disease occurs in an accelerated fashion in the donor heart after heart transplantation (TxCAD), but the cause is poorly understood. The risk of developing TxCAD is increased by cytomegalovirus (CMV) infection and decreased by use of calcium blockers. Our group observed that prophylactic administration of ganciclovir early after heart transplantation inhibited CMV illness, and we now propose to determine whether this therapy also prevents TxCAD. METHODS AND RESULTS: One hundred forty-nine consecutive patients (131 men and 18 women aged 48+/-13 years) were randomized to receive either ganciclovir or placebo during the initial 28 days after heart transplantation. Immunosuppression consisted of muromonab-CD3 (OKT-3) prophylaxis and maintenance with cyclosporine, prednisone, and azathioprine. Mean follow-up time was 4.7+/-1.3 years. In a post hoc analysis of this trial designed to assess efficacy of ganciclovir for prevention of CMV disease, we compared the actuarial incidence of TxCAD, defined by annual angiography as the presence of any stenosis. Because calcium blockers have been shown to prevent TxCAD, we analyzed the results by stratifying patients according to use of calcium blockers. TxCAD could not be evaluated in 28 patients because of early death or limited follow-up. Among the evaluable patients, actuarial incidence of TxCAD at follow-up (mean, 4.7 years) in ganciclovir-treated patients (n=62) compared with placebo (n=59) was 43+/-8% versus 60+/-10% (P<0.1). By Cox multivariate analysis, independent predictors of TxCAD were donor age >40 years (relative risk, 2.7; CI, 1.3 to 5.5; P<0.01) and no ganciclovir (relative risk, 2.1; CI, 1.1 to 5.3; P=0.04). Stratification on the basis of calcium blocker use revealed differences in TxCAD incidence when ganciclovir and placebo were compared: no calcium blockers (n=53), 32+/-11% (n=28) for ganciclovir versus 62+/-16% (n=25) for placebo (P<0.03); calcium blockers (n=68), 50+/-14% (n=33) for ganciclovir versus 45+/-12% (n=35) for placebo (P=NS). CONCLUSIONS: TxCAD incidence appears to be lower in patients treated with ganciclovir who are not treated with calcium blockers. Given the limitations imposed by post hoc analysis, a randomized clinical trial is required to address this issue.

Treatment of patients with advanced colorectal carcinomas with fluorouracil alone, high-dose leucovorin plus fluorouracil, or sequential methotrexate, fluorouracil, and leucovorin: a randomized trial of the Northern California Oncology Group.

We compared the effectiveness of fluorouracil (5-FU) alone (arm A), high-dose leucovorin plus 5-FU (arm B), and sequential methotrexate, 5-FU, and leucovorin (arm C) for treatment of patients with advanced colorectal carcinomas who had not received prior chemotherapy. Arm A consisted of infusions of 5-FU at 12 mg/kg/d intravenously (IV) for 5 days followed by weekly infusions of 5-FU at 15 mg/kg; arm B consisted of leucovorin infusions at 200 mg/m2/d IV plus infusions of 5-FU at 400 mg/m2/d IV on days 1 through 5 of a 28-day cycle; arm C consisted of methotrexate at 50 mg/m2 orally every 6 hours for five doses followed by infusions of 5-FU, 500 mg/m2 IV, and leucovorin, 10 mg/m2 orally, every 6 hours for five doses every other week. A total of 265 patients were entered into the trial, of whom 249 (94%) were fully evaluable. The objective response rate (complete [CR] plus partial [PR] responses) was 17.3% on arm A, 18.8% on arm B, and 19.8% on arm C (log-rank test, P greater than .4). The median time to failure was 138 days on arm A, 166 days on arm B, and 182 days on arm C (log-rank test, P values of arm A v B = .06; arm A v arm C = .04). Median survival was 345 days on arm A, 324 days on arm B, and 356 days on arm C (log-rank test, P greater than .4). Treatment with 5-FU alone was significantly more dose intensive and more toxic than either of the experimental combinations. The rates of grade 3 or greater nonhematologic toxicity were 42.3% on arm A, 24.3% on arm B, and 14.3% on arm C. Hematologic toxicity was milder but had the same pattern. This study indicates that these regimens of high-dose leucovorin plus 5-FU and sequential methotrexate, 5-FU, and leucovorin are not more effective than is 5-FU alone for treatment of patients with colorectal carcinomas when 5-FU is administered at high-dose intensity.

Stanford-Kaiser Permanente G1 study for clinical stage I to IIA Hodgkin's disease: subtotal lymphoid irradiation versus vinblastine, methotrexate, and bleomycin chemotherapy and regional irradiation.

PURPOSE: We have demonstrated that a relatively mild chemotherapy regimen, vinblastine, methotrexate, and bleomycin (VBM), and involved-field radiotherapy (IFRT) could substitute for extended-field radiotherapy in patients with favorable Hodgkin's disease (HD) who have been laparotomy-staged. The purpose of this study is to determine if VBM and regional radiotherapy can substitute for extended-field radiotherapy in favorable clinical stage (CS) I and II HD. PATIENTS AND METHODS: Seventy-eight patients with favorable CS I to II HD were randomly assigned to subtotal lymphoid irradiation (STLI) or VBM chemotherapy and regional radiotherapy. Randomization was stratified on the basis of age, sex, number of Ann Arbor sites, histology, and institution. Patients were evaluated for freedom from progressive HD, survival, and toxicity. Results were compared with the predecessor trial in pathologically staged patients. RESULTS: With a median follow-up period of 4 years, the rate of freedom from progressive HD was 92% (95% confidence interval [CI], 88% to 96%) for patients treated with STLI and 87% (95% CI, 81% to 93%) for patients treated with VBM and regional radiotherapy. Six of seven patients who relapsed are alive and in remission following successful second-line therapy. CONCLUSION: Given the caveat of a small number of patients, the results of extended-field radiotherapy and VBM and regional radiotherapy are comparable with a median follow-up period of 4 years. VBM serves as a paradigm to reduce late effects in favorable early-stage HD. We do not advocate its routine use in clinical practice, but instead encourage participation in clinical trials with the objective of maintaining efficacy while reducing toxicity in CS I and II HD.

Immunologic determinants of head and neck cancer response to induction chemotherapy.

Various measures of immune response were assessed prior to induction chemotherapy (intravenous [IV] cisplatin, fluorouracil [5-FU], and bleomycin) in 43 previously untreated head and neck cancer patients to derive a clinical response prediction model. These were parameters of functional cellular immunity (natural killer [NK] cell activity, lymphocyte blastogenesis response to mitogens), total lymphocyte and lymphocyte subset numbers and percentages, and circulating humoral immunity (total immunoglobulin, immunoglobulin classes, and C1q binding activity [C1q BA]). The C1q BA may reflect levels of circulating immune complexes within peripheral blood. The objective primary tumor response rate was 65% (16 complete responses and 12 partial responses). Univariate logistic regression analysis showed that failure to respond to therapy was significantly related to higher value (vis-à-vis response) of humoral immune parameters total immunoglobulin (Ig), P less than .01; IgG, P less than .01; and C1q BA, P less than .001. No association between cellular immune response measurements and response to chemotherapy was identified. By multivariate logistic regression analysis, only C1q BA levels were predictive of drug therapy responsiveness (P less than .001). Results extend our previous investigations regarding C1q BA measurement in head and neck cancer patients, and show that C1q BA levels add accuracy of prediction of subsequent chemotherapy response to that based solely on standard staging criteria and other parameters of immune status.

Genotype selection to rapidly breed congenic strains.

Congenic strains can now be constructed guided by the transmission of DNA markers. This allows not only selection for transmission of a desired, donor-derived differential region but also selection against the transmission of unwanted donor origin genomic material. The additional selection capacity should allow congenic strains to be produced in fewer generations than is possible with random backcrosses. Here, we consider modifications of a standard backcross breeding scheme to produce congenic mice by the inclusion of genotype-based selective breeding strategies. Simulation is used to evaluate the consequences of each strategy on the number of chromosomes that contain unwanted, donor-derived genetic material and the average length of this unwanted donor DNA for each backcross generation. Our prototypic strategy was to choose a single mouse to sire each generation using criteria designed to select against the transmission of chromosomes, other than the one containing the replacement genomic region, that contain any donor origin sequence at all. This chromosome elimination strategy resulted in an average of 16.4 chromosomes free of donor DNA in mice of the third backcross (N3) generation. A strategy based solely on positive selection for the replacement region required six backcross generations to achieve the same results.

Widespread cerebral gray matter volume deficits in schizophrenia.

Magnetic resonance imaging was used to investigate whether the structural brain differences commonly observed in patients with schizophrenia as compared with normal control subjects are specific to gray or white matter, and furthermore whether such abnormalities are localizable to circumscribed cortical regions. Accordingly, 22 patients meeting DSM-III-R criteria for schizophrenia and 20 healthy community volunteers, all 23 to 45 years old, received magnetic resonance imaging scans. Seven axial magnetic resonance imaging sections of 5-mm thickness were segmented into cerebrospinal fluid, gray matter, and white matter compartments and used for volumetric quantification. For the healthy control subjects, age correlated significantly with the percentage of all magnetic resonance imaging sections taken up by gray matter but not white matter. After correcting for the normal effect of age, the schizophrenic group was found to have significantly less gray matter than the control group but no difference in white matter; ventricular volume was 34% greater in the schizophrenic group. The schizophrenic group had less gray matter in all six cortical subregions analyzed; these differences attained statistical significance for all but the parietal measure. These findings have implications for studies of localized gray matter abnormalities and suggest that regional brain volume measurements need to be expressed in the context of possible widespread gray matter volume deficits in schizophrenia.

Neonatal immunization against gonadotropin-releasing hormone (GnRH) results in diminished GnRH secretion in adulthood.

The effects of neonatal immunization against GnRH were studied in sheep after they had reached adulthood (3-4 yr) and the antibody titers had fallen to undetectable levels. The immunized animals had small gonads, and the females did not have large follicles (>3 mm) or corpora lutea in their ovaries. Compared with controls, the immunized animals had low or nondetectable levels of LH and FSH in peripheral plasma, and the immunized animals generally failed to respond to a single i.v. GnRH challenge. After ovariectomy, the control ewes, but not the immunized ewes, showed an elevation in plasma LH and FSH levels. The sampling of hypophysial portal blood, with a newly described method, showed that the secretion of GnRH was reduced in the immunized animals, but the amount of GnRH in the median eminence was similar in the control and immunized ewes. The pituitary content of LH and FSH was reduced in the immunized ewes as was messenger RNA for the gonadotropin subunits and the GnRH receptor. These data indicate that neonatal immunization does not affect the synthesis of GnRH in adulthood but reduces the secretion of GnRH, causing long-term sterility in these animals.

Assay of aspirin and naproxen analgesia.

To establish the relative potency of naproxen and aspirin for oral analgesia, a 4-point, noncrossover bioassay with placebo control was undertaken with 197 patients. Subjective-response methods were used to determine two measures of postoperative analgesia over a period of 6 hr. With reasonable confidence for an oral analgesic assay, we found 220 mg of naproxen to be equivalent to 600 mg of aspirin for pain relief and 330 mg of naproxen to be equivalent to 600 mg of aspirin for decreased pain intensity.

Hypnotic efficacy of diphenhydramine, methapyrilene, and pentobarbital.

The antihistamines diphenhydramine and methapyrilene were compared with pentobarbital for hypnotic effect in two Veterans Administration Hospital populations using subjective-response methods. In the first part of the study, 60 mg and 180 mg of pentobarbital were compared with 50 mg and 150 mg of diphenhydramine. A positive dose-response relationship was obtained only for pentobarbital; neither dose of diphenhydramine was significantly different from 60 mg of pentobarbital for any response variable. In the second part of the study, 100 mg of pentobarbital, 50 mg of diphenhydramine, and 50 mg of diphenhydramine, and 50 mg of methapyrilene were compared with placebo. One hundred mg of pentobarbital and 50 mg of diphenhydramine were significantly different from placebo, but 50 mg of methapyrilene was not.

Effects of size and growth time of a murine sarcoma on its metastatic spread.

The effects of the size of an implanted tumor and of its time of growth on metastasis were examined in the same tumor grown under two different conditions. Tumors were implanted either in the untreated legs of mice or in legs that had been irradiated one day earlier. The radiation slowed the growth of tumors. When the tumors grew to predetermined diameters, the legs were excised and 20 days later the mice were examined for the presence of lung metastases. Equal changes in the time to excision of the tumors grown under the two conditions led to nearly equal changes in the proportions of animals with metastases. Tumor volume effects were not apparent in this consideration of changes in metastasis rates with time. This work reanalyses the data of that study using the variability in growth rates within a tumor growth condition to investigate the effect of tumor size on metastatic intensity. This intensity increased at least linearly with tumor volume for both irradiated and control animals. The finding of equal effect at equal growth times of the implanted tumors under the two growth conditions was confirmed but is due to: (1) metastatic intensity changing five times as rapidly with tumor size in the irradiated group as compared to the control group and (2) non-exponential retarded growth of the tumors in the control treatment group.