Categorizing a prognostic variable: review of methods, code for easy implementation and applications to decision-making about cancer treatments

Categorizing prognostic variables is essential for their use in clinical decision-making. Often a single cutpoint that stratifies patients into high-risk and low-risk categories is sought. These categories may be used for making treatment recommendations, determining study eligibility, or to control for varying patient prognoses in the design of a clinical trial.Methods used to categorize variables include: biological determination (most desirable but often unavailable); arbitrary selection of a cutpoint at the median value; graphical examination of the data for a threshold effect; and exploration of all observed values for the one which best separates the risk groups according to a chi-squared test. The last method, called the minimum p-value approach, involves multiple testing which inflates the type I error rates. Several methods for adjusting the inflated p-values have been proposed but remain infrequently used.Exploratory methods for categorization and the minimum p-value approach with its various p-value corrections are reviewed, and code for their easy implementation is provided. The combined use of these methods is recommended, and demonstrated in the context of two cancer-related examples which highlight a variety of the issues involved in the categorization of prognostic variables.     

Interferon-alfa as a comparative treatment for clinical trials of new therapies against advanced renal cell carcinoma.

PURPOSE: To define outcome data and prognostic criteria for patients with metastatic renal cell carcinoma (RCC) treated with interferon-alfa as initial systemic therapy. The data can be applied to design and interpretation of clinical trials of new agents and treatment programs against this refractory malignancy. PATIENTS AND METHODS: Four hundred sixty-three patients with advanced RCC administered interferon-alpha as first-line systemic therapy on six prospective clinical trials were the subjects of this retrospective analysis. Three risk categories for predicting survival were identified on the basis of five pretreatment clinical features by a stratified Cox proportional hazards model. RESULTS: The median overall survival time was 13 months. The median time to progression was 4.7 months. Five variables were used as risk factors for short survival: low Karnofsky performance status, high lactate dehydrogenase, low serum hemoglobin, high corrected serum calcium, and time from initial RCC diagnosis to start of interferon-alpha therapy of less than one year. Each patient was assigned to one of three risk groups: those with zero risk factors (favorable risk), those with one or two (intermediate risk), and those with three or more (poor risk). The median time to death of patients deemed favorable risk was 30 months. Median survival time in the intermediate-risk group was 14 months. In contrast, the poor-risk group had a median survival time of 5 months. CONCLUSION: Progression-free and overall survival with interferon-alpha treatment can be compared with new therapies in phase II and III clinical investigations. The prognostic model is suitable for risk stratification of phase III trials using interferon-alpha as the comparative treatment arm.     

Salvage chemotherapy for patients with advanced pure seminoma.

PURPOSE: We describe the response to conventional or high-dose salvage chemotherapy in patients with advanced seminoma who experience disease progression after receiving first-line platinum-based treatment. PATIENTS AND METHODS: Twenty-seven patients with progressive, advanced, pure seminoma were treated with salvage chemotherapy. Fifteen patients were treated with conventional-dose cisplatin-and-ifosfamide combination chemotherapy. Twelve patients were treated with high-dose chemotherapy followed by autologous stem-cell rescue. RESULTS: Fifteen patients (56%) achieved a complete response (CR), nine achieved CR with a conventional-dose cisplatin and ifosfamide program, and six experienced CR after high-dose chemotherapy. Fourteen patients (52%) are alive and disease-free, with 13 (48%) continuously disease-free at a median follow-up of 72 months. Twelve (57%) of 21 patients whose pretreatment tumors were studied morphologically were found to have seminoma with atypia. Eight patients underwent resection after salvage chemotherapy; six with histologic findings of necrotic debris/fibrosis alone are alive and disease-free at last follow-up. Both patients with viable seminoma found at surgery died of disease. CONCLUSION: Most patients with advanced seminoma are cured with standard first-line programs of cisplatin and etoposide with or without bleomycin. A small minority of patients with pure seminoma have resistant tumors and require salvage chemotherapy. In this setting, approximately 50% of patients with recurrent pure seminoma achieve durable CR with conventional or high-dose salvage chemotherapy. Identification of biologic markers to predict clinical outcome and an enhanced understanding of the basic biologic features of seminoma may lead to improvements in the management of this disease.     

Phase I trial of intravesical gemcitabine in bacillus Calmette-Guérin-refractory transitional-cell carcinoma of the bladder.

PURPOSE: The aim of this phase I study was to determine the safety and toxicity profile of gemcitabine administered as an intravesical agent in patients with transitional-cell carcinoma (TCC) of the bladder. PATIENTS AND METHODS: Patients with superficial bladder cancer refractory to intravesical bacillus Calmette-Guérin (BCG) therapy and refusing a cystectomy were considered eligible for the trial. Gemcitabine was given in the bladder for 1 hour twice weekly in 100 mL sodium chloride for a total of six treatments. After a 1-week break, a second course of six treatments over 3 weeks was given, followed by response assessment. Four dose levels were explored: 500 mg, 1,000 mg, 1,500 mg, and 2,000 mg. RESULTS: Eighteen patients completed therapy: three at 500 mg, six at 1,000 mg, three at 1,500 mg, and six at 2,000 mg. No grade 3 or 4 toxicity was observed at 500 mg. At 1,000 mg, three patients developed hematuria and one had a skin reaction resembling grade 3 hand-foot syndrome. Three patients at 1,500 mg had no grade 3 or 4 toxicity. Of six patients at 2,000 mg, one had grade 3 thrombocytopenia and neutropenia without infection. Seven patients had a complete response (negative cytology and posttreatment biopsy), and four patients had a mixed response (negative bladder biopsy but positive cytology). CONCLUSION: Gemcitabine has substantial activity as an intravesical agent in BCG-refractory TCC and warrants further investigation. Therapy given twice weekly was associated with minimal bladder irritation and tolerable myelosuppression. The recommended phase II dose for twice-weekly therapy is 2,000 mg.     

Role of angiotensin-converting enzyme inhibitor, lisinopril, on spermatozoal functions in rats

Angiotensin-converting enzyme is present in the male reproductive system but its role in the physiology of reproduction is not known. To see the effect of angiotensin-converting enzyme on spermatozoal functions, lisinopril, an angiotensin-converting enzyme inhibitor, was administered orally using two different doses (10 and 20 mg/kg/day) to rats. Both short-term (2 weeks) and long-term (6 weeks) effects of the drug were observed. Lisinopril treatment resulted in a marked decrease in sperm density, sperm motility and zona pellucida penetration. Acrosome reaction by spermatozoa obtained from drug-treated animals was significantly lower when compared with spermatozoa from normal animals.     

Long-term oncologic outcome following preoperative combined modality therapy and total mesorectal excision of locally advanced rectal cancer

OBJECTIVE: Our aims were to (1) determine the long-term oncologic outcome for patients with rectal cancer treated with preoperative combined modality therapy (CMT) followed by total mesorectal excision (TME), (2) identify factors predictive of oncologic outcome, and (3) determine the oncologic significance of the extent of pathologic tumor response. SUMMARY BACKGROUND DATA: Locally advanced (T3-4 and/or N1) rectal adenocarcinoma is commonly treated with preoperative CMT and TME. However, the long-term oncologic results of this approach and factors predictive of a durable outcome remain largely unknown. METHODS: Two hundred ninety-seven consecutive patients with locally advanced rectal adenocarcinoma at a median distance of 6 cm from the anal verge (range 0-15 cm) were treated with preoperative CMT (radiation: 5040 centi-Gray (cGy) and 5-fluorouracil (5-FU)-based chemotherapy) followed by TME from 1988 to 2002. A prospectively collected database was queried for long-term oncologic outcome and predictive clinicopathologic factors. RESULTS: With a median follow-up of 44 months, the estimated 10-year overall survival (OS) was 58% and 10 year recurrence-free survival (RFS) was 62%. On multivariate analysis, pathologic response >95%, lymphovascular invasion and/or perineural invasion (PNI), and positive lymph nodes were significantly associated with OS and RFS. Patients with a >95% pathologic response had a significantly improved OS (P = 0.003) and RFS (P = 0.002). CONCLUSIONS: Treatment of locally advanced rectal cancer with preoperative CMT followed by TME can provide for a durable 10-year OS of 58% and RFS of 62%. Patients who achieve a >95% response to preoperative CMT have an improved long-term oncologic outcome, a novel finding that deserves further study.     

A theoretical approach to choosing the minimum number of multiple tumors required for assessing treatment response

BACKGROUND AND OBJECTIVE: Most advanced cancer patients have multiple tumors. Because the multiple tumors are from the same patient, the tumor sizes are expected to be correlated and the information contained in each additional tumor might not always have significant 'added value' toward the response assessment. Needing to measure only a subset of tumors would reduce workload for the study radiologist but is expected to increase the variability in response outcome. We compute this increment in variability and find a procedure for choosing the minimum number (m) of tumors among some fixed maximum number (M) of correlated tumors that must be considered to ensure precision of at least as high as a specified proportion of the precision obtained if one were to measure all M tumors. METHOD: The ratio V(m)(R)/V(M)(R) = M2[m + (m2 - m)rho(ICC)]/m2[M + (M2 - M)rho(ICC)] quantifies the percentage increment in variance of the response R, where rho(ICC) is the intra-class between tumors within patient correlation coefficient. The procedure for choosing the minimum number of tumors is demonstrated using data for 42 cancer patients with 10 or more tumors. RESULTS: Using the criterion that >20% increase in variability due to selection of a subset out of M of 10 tumors is unacceptable, we find that m of 9, 6, 5, 3, and 2 tumors are needed when rho(ICC)=0.0 (no correlation), 0.2, 0.4, 0.6, and 0.8, respectively. If the criterion is made stricter to >10%, the number of tumors needed rise to 10, 8, 6, 4, and 3, respectively. For the example, 6 tumors out of 10 are found to provide sufficiently stable response categorization confirming the theoretical result. CONCLUSION: If cancer research community can agree on a percentage of variability in response outcome that is unacceptable, it is mathematically possible to recommend a minimum number of tumors that should be used for response assessment.