Estimation of the survival function for Gray's piecewise-constant time-varying coefficients model

Gray's extension of Cox's proportional hazards (PH) model for right-censored survival data allows for a departure from the PH assumption via introduction of time-varying regression coefficients (TVC). For this model estimation of the conditional hazard rate relies on the inclusion of penalized splines. Cubic penalized splines tend to be unstable in the right tail of the distribution and thus quadratic, linear and piecewise-constant penalized splines may be a favourable choice. We derive a survival function estimator for one important member of the class of TVC models--a piecewise-constant time-varying coefficients (PC-TVC) model. Using the first-order Taylor series approximation we also derive an estimate for the variance of the log-transformed and log(-log)-transformed survival function, which in turn leads to estimated confidence limits on the corresponding scales of the survival function. Accuracy in estimating underlying survival times and survival quantiles is assessed for both Cox's and Gray's PC-TVC model using a simulation study featuring scenarios violating the PH assumption. Finally, an example of the estimated survival functions and the corresponding confidence limits derived from Cox's PH and Gray's PC-TVC model, respectively, is presented for a liver transplant data set.     

Chromosomal aberrations in lymphocytes of healthy subjects and risk of cancer

There is evidence that increased frequency of chromosomal aberration (CA) in peripheral blood lymphocytes is a predictor of cancer, but further data are needed to better characterize CA as marker of cancer risk. From the archives of 15 laboratories we gathered cytogenetic records of 11,834 subjects who were free of cancer at the moment of blood drawing and who underwent cytogenetic examination for preventive purposes in the Czech Republic during 1975-2000. We linked these records to the national cancer registry, revealing a total of 485 cancer cases. Subjects were classified according to the percentiles of CA distribution within each laboratory as low (0-33rd percentile), medium (34-66th percentile), and high (66-100th percentile). Subjects were further classified by occupational exposure and by subclass of CA. We found a significant association between the overall cancer incidence and the presence of chromosome-type aberrations [relative risk (RR) for high vs. low CA level = 1.24; 95% confidence interval (CI), 1.03-1.50] but not chromatid-type aberrations. Stomach cancer showed a strong association with frequency of total CA (RR = 7.79; 95% CI, 1.01-60.0). The predictivity of CA observed in subjects exposed to various classes of carcinogens did not significantly differ from the group of nonexposed subjects. This study contributes to validation of CA as a predictive marker of cancer risk, in particular, of stomach cancer; the association between CA frequency and cancer risk might be limited to chromosome-type aberrations.     

Pigmented solid-pseudopapillary neoplasm of the pancreas

A hitherto unrecognized variant of solid-pseudopapillary neoplasm of the pancreas is reported. The tumor presented in the pancreatic head of a 57-year-old female patient. It was a well-circumscribed, encapsulated nodule measuring 27 mm in diameter, with variegated yellow to brown and gray cut surface. Histologically, the neoplasm was composed of uniform polyhedral cells arranged around delicate fibrovascular cores retaining their solid pattern in the periphery, whereas central parts of the tumor were characterized by the formation of papillae and smaller pseudocysts. Neither mitotic activity nor invasive growth were found. Immunohistochemically, tumor cells were positive for vimentin, neuron-specific enolase, and CD56, whereas they were negative in reactions with antibodies directed against other neuroendocrine markers, cytokeratins, melanocytic markers, and pancreatic amylase. In addition to these typical findings, intracellular pigmented granules were found in the darker brown zones of the tumor. They were positively stained in periodic acid-Schiff reaction after diastase digestion, sudan black B, and in Schmorl stain. In contrast, they were not stained with Fontana-Masson, Ziehl-Neelsen, and Perls stains. Ultrastructurally, the pigment consisted of dense granules with lipid droplets resembling modified lysosomes. These results exclude the possibility of a melanogenic nature of the pigment and instead determine it as lipofuscin.     

Two interesting methods of estimation of the diagnosis uncertainty

It's very important to estimate the measure of uncertainty of data in the case of diagnosis of disease. We recommend two methods with help fuzzy interpretation of disease data.     

Screening detected celiac disease in children with type 1 diabetes mellitus: effect on the clinical course (a case control study)

OBJECTIVE: To investigate clinical and metabolic characteristics of diabetic children with screening detected celiac disease in a multicenter case-control study. METHODS: Cases: 98 diabetic patients were diagnosed as having silent celiac disease by screening with endomysial antibodies and subsequent biopsy. Controls: two controls in the same center were chosen, (stratified by age and age-at-diabetes onset) who were negative for endomysial antibodies (n = 195). Height, weight, HbA1c, insulin dosage and acute complications were documented for at least 1 year of follow up. RESULTS: Mean age of diabetes manifestation was 6.5 +/- 4.1 years and diagnosis of celiac disease was made at 10.0 +/- 5.4 years. Biopsy showed total or subtotal mucosal atrophy in 74 patients. The mean observation period after the diagnosis of celiac disease was 3.3 +/- 1.9 years. Mean HbA1c levels were similar between cases and controls (8.63% +/- 1.45% versus 8.50% +/- 1.39%; P = 0.35). There was also no difference in the frequency of severe hypoglycemia, ketoacidosis and the applied insulin dosage (P = 0.45). Body mass index-standard deviation score at celiac disease diagnosis (0.57 +/- 1.24 versus 0.52 +/- 1.07) and height-standard deviation score (0.14 +/- 1.13 versus 0.30 +/- 0.95) did not differ between cases and controls. After diagnosis of celiac disease, weight gain was diminished in boys with celiac disease compared with their controls (P < 0.05). Female cases also had a lower body mass index than female controls (P = 0.067). CONCLUSION: In a cohort of diabetic children, silent celiac disease had no obvious effect on metabolic control but negatively influenced weight gain.