Frederick P. Li

Human keratinocytes that express hTERT and also bypass a p16(INK4a)-enforced mechanism that limits life span become immortal yet retain normal growth and differentiation characteristics.

ABSTRACT Normal human cells exhibit a limited replicative life span in culture, eventually arresting growth by a process termed senescence. Progressive telomere shortening appears to trigger senescence in normal human fibroblasts and retinal pigment epithelial cells, as ectopic expression of the telomerase catalytic subunit, hTERT, immortalizes these cell types directly. Telomerase expression alone is insufficient to enable certain other cell types to evade senescence, however. Such cells, including keratinocytes and mammary epithelial cells, appear to require loss of the pRB/p16INK4a cell cycle control mechanism in addition to hTERT expression to achieve immortality. To investigate the relationships among telomerase activity, cell cycle control, senescence, and differentiation, we expressed hTERT in two epithelial cell types, keratinocytes and mesothelial cells, and determined the effect on proliferation potential and on the function of cell-type-specific growth control and differentiation systems. Ectopic hTERT expression immortalized normal mesothelial cells and a premalignant, p16INK4a-negative keratinocyte line. In contrast, when four keratinocyte strains cultured from normal tissue were transduced to express hTERT, they were incompletely rescued from senescence. After reaching the population doubling limit of their parent cell strains, hTERT+ keratinocytes entered a slow growth phase of indefinite length, from which rare, rapidly dividing immortal cells emerged. These immortal cell lines frequently had sustained deletions of the CDK2NA/INK4A locus or otherwise were deficient in p16INK4a expression. They nevertheless typically retained other keratinocyte growth controls and differentiated normally in culture and in xenografts. Thus, keratinocyte replicative potential is limited by a p16INK4a-dependent mechanism, the activation of which can occur independent of telomere length. Abrogation of this mechanism together with telomerase expression immortalizes keratinocytes without affecting other major growth control or differentiation systems.

Bone sarcomas linked to radiotherapy and chemotherapy in children

We estimated the risk of subsequent bone cancer among 9170 patients who had survived two or more years after the diagnosis of a cancer in childhood. As compared with the general population, the patients had a relative risk of 133 (95 percent confidence interval, 98 to 176) and a mean (+/- SE) 20-year cumulative risk of 2.8 +/- 0.7 percent. Detailed data on treatment were obtained on 64 patients in whom bone cancer developed after childhood cancer. As compared with 209 matched controls who had survived cancer in childhood but who did not have bone cancer later, patients who had had radiation therapy had a 2.7-fold risk (95 percent confidence interval, 1.0 to 7.7) and a sharp dose-response gradient reaching a 40-fold risk after doses to the bone of more than 6000 rad. The relative dose-response effect among patients who had been treated for retinoblastoma resembled that among patients with all other types of initial tumors, although the cumulative risk of bone cancer in the retinoblastoma group was higher. Similar numbers of patients were treated with orthovoltage and megavoltage; the patterns of risk among categories of doses did not differ according to the type of voltage. After adjustment for radiation therapy, treatment with alkylating agents was also linked to bone cancer (relative risk, 4.7; 95 percent confidence interval, 1.0 to 22.3), with the risk increasing as cumulative drug exposure rose. We conclude that both radiotherapy and chemotherapy with alkylating agents for childhood cancer increase the subsequent risk of bone cancer.

Hereditary renal-cell carcinoma associated with a chromosomal translocation.

MANY forms of human cancer tend to occur in families.1 Environmental causes of familial cancer often cannot be identified, and, by exclusion, a hereditary mechanism is postulated on the basis of pe...

Cancer Incidence After Retinoblastoma: Radiation Dose and Sarcoma Risk

CONTEXT There is a substantial risk of a second cancer for persons with hereditary retinoblastoma, which is enhanced by radiotherapy. OBJECTIVE To examine long-term risk of new primary cancers in survivors of childhood retinoblastoma and quantify the role of radiotherapy in sarcoma development. DESIGN Cohort incidence study of patients with retinoblastoma followed for a median of 20 years, and nested case-control study of a radiation dose-response relationship for bone and soft tissue sarcomas. SETTING/PARTICIPANTS A total of 1604 patients with retinoblastoma who survived at least 1 year after diagnosis, identified from hospital records in Massachusetts and New York during 1914 to 1984. RESULTS Incidence of subsequent cancers was statistically significantly elevated only in the 961 patients with hereditary retinoblastoma, in whom 190 cancers were diagnosed, vs 6.3 expected in the general population (relative risk [RR], 30 [95% confidence interval, 26-47]). Cumulative incidence (+/-SE) of a second cancer at 50 years after diagnosis was 51.0% (+/-6.2%) for hereditary retinoblastoma, and 5.0% (+/-3.0%) for nonhereditary retinoblastoma. All 114 sarcomas of diverse histologic types occurred in patients with hereditary retinoblastoma. For soft tissue sarcomas, the RRs showed a stepwise increase at all dose categories, and were statistically significant at 10 to 29.9 Gy and 30 to 59.9 Gy. A radiation risk for all sarcomas combined was evident at doses above 5 Gy, rising to 10.7-fold at doses of 60 Gy or greater (P<.05). CONCLUSIONS Genetic predisposition has a substantial impact on risk of subsequent cancers in retinoblastoma patients, which is further increased by radiation treatment. A radiation dose-response relationship is demonstrated for all sarcomas and, for the first time in humans, for soft tissue sarcomas. Retinoblastoma patients should be examined for new cancers and followed into later life to determine whether their extraordinary cancer risk extends to common cancers of adulthood.

Germline Mutations of the p53 Tumor-Suppressor Gene in Children and Young Adults with Second Malignant Neoplasms

BACKGROUND Acquired mutations in the p53 tumor-suppressor gene have been detected in several human cancers, including colon, breast, and lung cancer. Inherited mutations (transmitted through the germline) of this gene can underlie the Li-Fraumeni syndrome, a rare familial association of breast cancer in young women, childhood sarcomas, and other malignant neoplasms. We investigated the possibility that p53 mutations in the germline are associated with second primary cancers that arise in children and young adults who would not be considered as belonging to Li-Fraumeni families. METHODS Genomic DNA was extracted from the blood leukocytes of 59 children and young adults with a second primary cancer. The polymerase chain reaction, in combination with denaturant-gel electrophoresis and sequencing, was used to identify p53 gene mutations. RESULTS Mutations of p53 that changed the predicted amino acid sequence were identified in leukocyte DNA from 4 of the 59 patients (6.8 percent). In three cases, the mutations were identical to ones previously found in the p53 gene. The fourth mutation was the first germline mutation to be identified in exon 9, at codon 325. Analysis of leukocyte DNA from close relatives of three of the patients indicated that the mutations were inherited, but cancer had developed in only one parent at the start of the study. CONCLUSIONS These findings identify an important subgroup of young patients with cancer who carry germline mutations in the p53 tumor-suppressor gene but whose family histories are not indicative of the Li-Fraumeni syndrome. The early detection of such mutations would be useful not only in treating these patients, but also in identifying family members who may be at high risk for the development of tumors.

Risk of New Cancers After Radiotherapy in Long-Term Survivors of Retinoblastoma: An Extended Follow-Up

PURPOSE Many children diagnosed with retinoblastoma (Rb) survive into adulthood and are prone to subsequent cancers, particularly hereditary patients, who have germline Rb-1 mutations. We have extended the follow-up of a large cohort of Rb patients for 7 more years to provide new information on the risk of additional cancers after radiotherapy in long-term survivors. PATIENTS AND METHODS We analyzed the risk of new cancers through 2000 in 1,601 Rb survivors, diagnosed from 1914 to 1984, at two US medical centers. The standardized incidence ratio (SIR) was calculated as the ratio of the observed number of cancers after hereditary and nonhereditary Rb to the expected number from the Connecticut Tumor Registry. The cumulative incidence of a new cancer after hereditary and nonhereditary Rb and radiotherapy was calculated with adjustment for competing risk of death. RESULTS Subsequent cancer risk in 963 hereditary patients (SIR, 19; 95% CI, 16 to 21) exceeded the risk in 638 nonhereditary Rb patients (SIR, 1.2; 95% CI, 0.7 to 2.0). Radiation further increased the risk of another cancer in hereditary patients by 3.1-fold (95% CI, 2.0 to 5.3). Hereditary patients continued to be at significantly increased risk for sarcomas, melanoma, and cancers of the brain and nasal cavities. The cumulative incidence for developing a new cancer at 50 years after diagnosis of Rb was 36% (95% CI, 31% to 41%) for hereditary and 5.7% (95% CI, 2.4% to 11%) for nonhereditary patients. CONCLUSION Hereditary Rb predisposes to a variety of new cancers over time, with radiotherapy further enhancing the risk of tumors arising in the radiation field.

Ovarian failure in long-term survivors of childhood malignancy

The frequency and causes of ovarian failure among 182 long-term survivors of childhood cancer were examined. Twenty-two patients (12%) had ovarian failure. Ovarian failure was found in 17 of 25 patients (68%) who had both ovaries within abdominal radiotherapy fields, in five of 35 patients (14%) whose ovaries were at the edge of the treatment field, and in none of 122 patients with one or both ovaries outside of an abdominal treatment field (p < 10(-4)). The odds for ovarian failure in patients with both ovaries in the field are 19.7 higher than those for other irradiated patients (95% confidence interval, 5.3 to 72.8). Covariate and multivariate analyses of tumor type, age at diagnosis, duration of follow-up, abdominal tumor surgery, abdominal radiotherapy, number of chemotherapeutic agents administered, and cumulative doses of several drugs revealed that the location of the ovaries relative to radiation treatment fields was the only risk factor for subsequent ovarian failure.

Germline p53 mutations are frequently detected in young children with rhabdomyosarcoma.

We investigated the possibility that a proportion of children with sporadic rhabdomyosarcoma (RMS) carry constitutional mutations of the p53 tumor suppressor gene. 33 patients with sporadic RMS at two large outpatient pediatric oncology clinics submitted blood samples. Genomic DNA was extracted from peripheral blood leukocytes and PCR was used to amplify exons 2-11 of the p53 gene. Amplified genomic DNA was screened for the presence of germline p53 mutations using single-strand conformation polymorphism (SSCP) analysis. The DNA sequence of those samples that showed aberrant migration of bands on SSCP analysis was determined to identify the precise nature of the gene mutations. Patient records were reviewed to assess clinical correlates of the mutant p53 carrier state. Heterozygous constitutional mutations were detected in 3/33 patient samples screened. Two of these missense mutations are located in exon 7 and one in exon 8 of the p53 gene. The presence of mutations was not correlated with tumor histology, stage, or site. However, an association between young age at diagnosis and presence of a constitutional p53 mutation was noted: 3/13 children under the age of 3 yr at diagnosis carried mutations, whereas none of 20 children over 3 yr of age at diagnosis harbored a detectable constitutional mutation. These results in children with RMS corroborates previous findings in other clinical settings suggesting that the mutant p53 carrier state may predispose individuals to malignancy at an early age. Although this study did not assess whether the mutations were preexisting or new germline alterations, assessment of close relatives of RMS patients for cancer risk and predictive genetic testing may be indicated.

Predictors of Smoking Initiation and Cessation Among Childhood Cancer Survivors: A Report From the Childhood Cancer Survivor Study

PURPOSE To examine the determinants of smoking behavior among participants in the Childhood Cancer Survivors Study (CCSS). METHODS This retrospective cohort survey study was conducted among 9,709 childhood cancer survivors. Main outcomes included smoking initiation and cessation. RESULTS Twenty-eight percent of patients reported ever smoking and 17% reported being current smokers. Standardized to United States population rates, the observed to expected (O/E) ratios and corresponding 95% confidence limits (95% CL) of cigarette smoking were 0.72 (95% CL, 0.69, 0.75) among all survivors and 0.71 (95% CL, 0.68 to 0.74) and 0.81 (95% CL, 0.70, 0.93) among whites and nonwhites, respectively. Significantly lower O/E ratios were present among both males (O/E, 0.73) and females (O/E, 0.70). Factors independently associated with a statistically significant relative risk of smoking initiation included older age at cancer diagnosis, lower household income, less education, not having had pulmonary-related cancer treatment, and not having had brain radiation. Blacks were less likely to start smoking. Survivors who smoked were significantly more likely to quit (O/E, 1.22; 95% CL, 1.15, 1.30). Among ever-smokers, factors associated with the likelihood of being a current smoker included age less than 13 years at smoking initiation, less education, and having had brain radiation; those age less than 3 years at cancer diagnosis were significantly more likely to be ex-smokers. CONCLUSIONS Although survivors in the CCSS cohort seem to be smoking at rates below the general population, interventions are needed to prevent smoking initiation and promote cessation in this distinct population.

Second malignant tumors after cancer in childhood

Studies were made of the development of second malignant tumors in children treated at the Sidney Farber Cancer Institute. In 1973 a retrospective analysis identified second cancers in 15 of 410 patients who survived a childhood cancer. During the period 5‐24 years after diagnosis of the first cancer, the cumulative probability of developing a new cancer was 12%. This frequency was approximately 20‐fold higher than the expected rate for the general population. Prospective study of the series since 1973 has identified a second primary cancer in five additional patients. The majority of second cancers were in the field of prior radiotherapy, and were attributable to the oncogenic effect of radiation. Genetic susceptibility factors were identified in individual patients.