Quantitative mathematical modeling of clinical brain metastasis dynamics in non-small cell lung cancer.

Brain metastases (BMs) are associated with poor prognosis in non-small cell lung cancer (NSCLC), but are only visible when large enough. Therapeutic decisions such as whole brain radiation therapy would benefit from patient-specific predictions of radiologically undetectable BMs. Here, we propose a mathematical modeling approach and use it to analyze clinical data of BM from NSCLC. Primary tumor growth was best described by a gompertzian model for the pre-diagnosis history, followed by a tumor growth inhibition model during treatment. Growth parameters were estimated only from the size at diagnosis and histology, but predicted plausible individual estimates of the tumor age (2.1-5.3 years). Multiple metastatic models were further assessed from fitting either literature data of BM probability (n = 183 patients) or longitudinal measurements of visible BMs in two patients. Among the tested models, the one featuring dormancy was best able to describe the data. It predicted latency phases of 4.4-5.7 months and onset of BMs 14-19 months before diagnosis. This quantitative model paves the way for a computational tool of potential help during therapeutic management.

Universal screening to identify gestational diabetes: a multi-centre study in the North of England.

We conducted an audit of treatment and outcomes in 116 women with gestational diabetes. These women received intense monitoring and high levels of medical and obstetric intervention. 24% would not have been identified by risk factor based screening. Cost effective strategies to identify all women with gestational diabetes are needed.

[Analysis of results of excerpts of generalized parametric indicators of facet classification of occupations in medicine, practical, industrial pharmacy, cosmetology and major of related occupations introduced to State classifiers 003:2010].

A comparative analysis of the content and the list of codified occupations (CO) of State classifiers (SC) of occupations SC 003-95 and SC 003:2010 (total 15 000 positions) is considered. Found that the number of corresponding CO in the SC 003-95 consist of 906 items including 57 of Vol. 78 "Care of public health", as well as in SC 003:2010 - 799 and 59 respectively.

Prevalence and nature of anaemia in a prospective, population-based sample of people with diabetes: Teesside anaemia in diabetes (TAD) study.

AIMS: Anaemia occurs in 25% of people attending hospital diabetes clinics, but this may not be representative of all people with diabetes. We aimed to determine the prevalence of anaemia in a prospective population-based sample stratified by estimated glomerular filtration rate (eGFR) using the 4-point Modification of Diet in Renal Disease (MDRD) formula. METHODS: All 7331 patients on our district register were stratified by eGFR. Seven hundred and thirty were approached by letter on two occasions. Two hundred and thirty-four (32%) returned questionnaires and blood samples. Responders (R), non-responders (NR) and the whole cohort (C) were similar: mean +/- sd age R 61.7 +/- 12.7 years; NR 61.3 +/- 15.1 years; C 61.8 +/- 14.2 years; diabetes duration R 8.8 +/- 8.6 years; NR 8.2 +/- 7.9 years; C 7.5 +/- 7.8 years, Type 1 diabetes R 10.1%, NR 10.8%, C 9.4%. Anaemia was defined using World Health Organization criteria: haemoglobin < 13 g/dl for men, < 12 g/dl for women. RESULTS: Previously undiagnosed anaemia was present in 15% of the whole group, 36% with eGFR < 60 ml/min per 1.73 m(2) and 9% of those with eGFR > 60 ml/min per 1.73 m(2). Anaemia was as a result of erythropoietin deficiency in 34%, abnormal haematinics in 40% and was unexplained in 26% of patients. Five per cent of the patients had anaemia below the treatment threshold of 11 g/dl. CONCLUSIONS: The prevalence of unrecognized anaemia in population-based cohorts is lower than that in hospital-based studies. Current clinical surveillance in the UK is failing to detect anaemia in stage 3-5 chronic kidney disease (eGFR < 60 ml/min per 1.73 m(2)) and current guidelines will not detect 9% of diabetic patients with anaemia and an eGFR > 60 ml/min per 1.73 m(2).

A quality assurance exercise to evaluate the accuracy and reproducibility of chromogenic in situ hybridisation for HER2 analysis in breast cancer.

BACKGROUND: Chromogenic in situ hybridisation (CISH) is an alternative to immunohistochemistry or FISH for the assessment of HER2 oncogene status in breast cancer. Although CISH is being used increasingly in routine diagnostics, there are no established inter-laboratory quality assurance programmes for this test. METHODS: The reproducibility of HER2 CISH analysis was assessed when performed by seven different centres that use the test routinely in diagnostic service. RESULTS: The results from 28 cases showed overall concordance of 98.5% (192/195 tests; kappa coefficient 0.91). One of the discrepancies was due to the invasive carcinoma having been cut out in the sections received by two of the centres, and the other two were in the non-amplified/equivocal/low-amplified category. CONCLUSION: This is believed to be the first report of a quality assurance study assessing laboratories that use HER2 CISH routinely in clinical diagnostics. The results show that CISH is a robust technique providing a suitable assay for the frontline testing of HER2 status in breast cancer.

Borderline breast core needle histology: predictive values for malignancy in lesions of uncertain malignant potential (B3).

Breast core needle biopsy (CNB) is an accurate test but may result in borderline histology (lesions of uncertain malignant potential or B3). This is an evaluation of the largest series (to date) of B3 histology, which focuses on estimating positive predictive values (PPV) for malignancy. We identified all B3 CNBs over a 10-year period in a single institution (N=372) from a series of 4035 consecutive needle biopsies. We describe the imaging findings, and report excision histology outcomes (N=279) and category-specific PPV for B3 lesions using two approaches including estimates based on subjects who had either excision or follow-up (N=328). B3 represented 9.2% of all CNB results. Excision histology was benign in 181 (64.9%) and malignant in 98 (35.1%) subjects (61 ductal carcinoma in situ, 37 invasive carcinoma). Positive predictive value for malignancy (based on excision histology) was 35.1% (95% CI: 29.5-40.7) and PPV (based on excision or review) was 29.9% (95% CI: 24.9-34.8). Lesion-specific PPV (estimates in parentheses for excision or follow-up) was atypical ductal hyperplasia 44.7% (40.6%); lobular intraepithelial neoplasia 60.9% (58.3%); papillary lesion 22.7% (15.9%); radial scar 16.7% (12.3%); phyllodes tumour 12.5% (12.5%); and B3 not specified 20.0%. Approximately one-third of CNB results classified as B3 are malignant on excision, and the likelihood of malignancy varies substantially between specific lesion groups. Whereas cases may be selectively managed without surgery, the majority warrant excision biopsy based on our estimates. Research is needed to improve differentiation between malignant and benign diseases in B3 lesions using diagnostic or predictive methods.

A risk index for early node-negative breast cancer.

BACKGROUND: This study compared the application of the St Gallen 2001 classification with a risk index developed at the New South Wales Breast Cancer Institute (BCI Index) for women with node-negative breast cancer treated without adjuvant systemic therapy. METHODS: The BCI risk categories were constructed by identifying combinations of prognostic indicators that produced homogeneous low-, intermediate- and high-risk groups using the same variables as in the St Gallen classification. RESULTS: The BCI low-risk category consisted of women aged 35 years or more with a grade 1 oestrogen receptor (ER)-positive tumour 20 mm or less in diameter, or with a grade 2 ER-positive tumour of 15 mm or less. This category constituted 40.1 per cent of patients, with a 10-year distant relapse-free survival (DRFS) rate of 97.2 per cent. The BCI intermediate-risk category included women aged 35 years or more with a grade 2 ER-positive tumour of diameter 16-20 mm, or a grade 1 or 2 ER-negative tumour measuring 15 mm or less, and comprised 12.1 per cent of the women, with a 10-year DRFS rate of 88 per cent. The high-risk category comprised 47.7 per cent of women, with a 10-year DRFS rate of 68.4 per cent. CONCLUSION: If confirmed in other data sets, the BCI Index may be used to identify women at low risk of distant relapse (2.8 per cent at 10 years) who are unlikely to benefit from adjuvant systemic therapy, and women at intermediate risk of distant relapse (12 per cent at 10 years) in whom the benefit of adjuvant systemic therapy is small.

Predicting the HER2 status of breast cancer from basic histopathology data: an analysis of 1500 breast cancers as part of the HER2000 International Study.

The tests that are currently available for the measurement of overexpression of the human epidermal growth factor-2 (HER2) in breast cancer have shown considerable problems in accuracy and interlaboratory reproducibility. Although these problems are partly alleviated by the use of validated, standardised 'kits', there may be considerable cost involved in their use. Prior to testing it may therefore be an advantage to be able to predict from basic pathology data whether a cancer is likely to overexpress HER2. In this study, we have correlated pathology features of cancers with the frequency of HER2 overexpression assessed by immunohistochemistry (IHC) using HercepTest (Dako). In addition, fluorescence in situ hybridisation (FISH) has been used to re-test the equivocal cancers and interobserver variation in assessing HER2 overexpression has been examined by a slide circulation scheme. Of the 1536 cancers, 1144 (74.5%) did not overexpress HER2. Unequivocal overexpression (3+ by IHC) was seen in 186 cancers (12%) and an equivocal result (2+ by IHC ) was seen in 206 cancers (13%). Of the 156 IHC 3+ cancers for which complete data was available, 149 (95.5%) were ductal NST and 152 (97%) were histological grade 2 or 3. Only 1 of 124 infiltrating lobular carcinomas (0.8%) showed HER2 overexpression. None of the 49 'special types' of carcinoma showed HER2 overexpression. Re-testing by FISH of a proportion of the IHC 2+ cancers showed that only 25 (23%) of those assessable exhibited HER2 gene amplification, but 46 of the 47 IHC 3+ cancers (98%) were confirmed as showing gene amplification. Circulating slides for the assessment of HER2 score showed a moderate level of agreement between pathologists (kappa 0.4). As a result of this study we would advocate consideration of a triage approach to HER2 testing. Infiltrating lobular and special types of carcinoma may not need to be routinely tested at presentation nor may grade 1 NST carcinomas in which only 1.4% have been shown to overexpress HER2. Testing of these carcinomas may be performed when HER2 status is required to assist in therapeutic or other clinical/prognostic decision-making. The highest yield of HER2 overexpressing carcinomas is seen in the grade 3 NST subgroup in which 24% are positive by IHC.

Mapping of quantitative trait loci for field resistance to Fusarium head blight in an European winter wheat.

Fusarium head blight (FHB) caused by Fusarium culmorum is an economically important disease of wheat that may cause serious yield and quality losses under favorable climate conditions. The development of disease-resistant cultivars is the most effective control strategy. Worldwide, there is heavy reliance on the resistance pool originating from Asian wheats, but excellent field resistance has also been observed among European winter wheats. The objective of this study was to map and characterize quantitative traits loci (QTL) of resistance to FHB among European winter wheats. A population of 194 recombinant inbred lines (RILs) was genotyped from a cross between two winter wheats Renan (resistant)/Récital (susceptible) with microsatellites, AFLP and RFLP markers. RILs were assessed under field conditions For 3 years in one location. Nine QTLs were detected, and together they explained 30-45% of the variance, depending on the year. Three of the QTLs were stable over the 3 years. One stable QTL, QFhs.inra.2b, was mapped to chromosome 2B and two QTLs QFhs.inra.5a2 and QFhs.inra5a3, to chromosome 5A; each of these QTLs explained 6.9-18.6% of the variance. Other QTLs were identified on chromosome 2A, 3A, 3B, 5D, and 6D, but these had a smaller effect on FHB resistance. One of the two QTLs on chromosome 5A was linked to gene B1 controlling the presence of awns. Overlapping QTLs for FHB resistance were those for plant height or/and flowering time. Our results confirm that wheat chromosomes 2A, 3A, 3B, and 5A carry FHB resistance genes, and new resistance factors were identified on chromosome arms 2BS and 5AL. Markers flanking these QTLs should be useful tools for combining the resistance to FHB of Asian and European wheats to increase the resistance level of cultivars.

Use of the St Gallen classification for patients with node-negative breast cancer may lead to overuse of adjuvant chemotherapy.

BACKGROUND: The 1998 St Gallen classification was devised to guide clinicians in the use of adjuvant systemic therapy for women with early breast cancer. In this study, the classification was applied to a historical group of patients with node-negative breast cancer who were treated without adjuvant therapy. METHODS: The St Gallen classification was applied to 421 women with breast cancer treated with conservative surgery and radiotherapy alone between 1979 and 1994. Primary tumour characteristics were reviewed centrally. RESULTS: When the most stringent version of the St Gallen classification was applied (grade 2 or 3 tumours classified as "high risk"), only 10 per cent of patients were "low risk", with a 10-year distant relapse-free survival (DRFS) rate of 100 per cent, and 15 per cent were at "intermediate risk" (10-year DRFS rate of 94 per cent). The high-risk group (75 per cent of women) had a 10-year DRFS rate of 77 per cent (P < 0.01). If the St Gallen classification had been applied to all patients in this series who were aged less than 70 years, up to 91 per cent would have been recommended to have chemotherapy. CONCLUSION: The St Gallen classification is an inaccurate measure of prognosis for patients with node-negative breast cancer and should be used with caution.

Treatment implications of a positive sentinel lymph node biopsy for patients with early-stage breast carcinoma.

BACKGROUND: Sentinel lymph node (SLN) mapping and biopsy is emerging as an alternative to axillary lymph node dissection (ALND) in determining the lymph node status of patients with early-stage breast carcinoma. The hypothesis of the technique is that the SLN is the first lymph node in the regional lymphatic basin that drains the primary tumor. Non-SLN (NSLN) metastasis in the axilla is unlikely if the axillary SLN shows no tumor involvement, and, thus, further axillary interference may be avoided. However, the optimal treatment of the axilla in which an SLN metastasis is found requires ongoing evaluation. The objectives of this study were to evaluate the predictors for NSLN metastasis in the presence of a tumor-involved axillary SLN and to examine the treatment implications for patients with early-stage breast carcinoma. METHODS: Between June 1998 and May 2000, 167 patients participated in the pilot study of SLN mapping and biopsy at Westmead Hospital. SLNs were identified successfully and biopsied in 140 axillae. All study patients also underwent ALND. The incidence of NSLN metastasis in the 51 patients with a SLN metastasis was correlated with clinical and pathologic characteristics. RESULTS: Of 51 patients with a positive SLN, 24 patients (47%) had NSLN metastases. The primary tumor size was the only significant predictor for NSLN involvement. NSLN metastasis occurred in 25% of patients (95% confidence interval [95%CI], 10-47%) with a primary tumor size 20 mm (P = 0.005). The size of the SLN metastasis was not associated significantly with NSLN involvement. Three of 7 patients (43%) with an SLN micrometastasis (< 1 mm) had NSLN involvement compared with 38 of 44 patients (48%) with an SLN macrometastasis (> or = 1 mm). CONCLUSIONS: The current study did not identify a subgroup of SLN positive patients in whom the incidence of NSLN involvement was low enough to warrant no further axillary interference. At present, a full axillary dissection should be performed in patients with a positive SLN.

Complex sclerosing lesion: the lesion is complex, the management is straightforward.

BACKGROUND: Complex sclerosing lesion (CSL) and its smaller counterpart, the radial scar (RS), are frequently seen pathological entities. They are clinically asymptomatic and, prior to the implementation of mammographic screening, were most commonly found incidentally during pathological examination of other biopsied lesions. Complex sclerosing lesions are being detected regularly on mammograms due to widespread screening; many of their features resemble those of malignancy. Management varies and has been controversial. METHODS: Twenty-three cases of CSL detected during the first prevalent round of screening at BreastScreen Western Sydney (from February 1993 until June 1995) are presented and reviewed. Assessment was by a combination of radiological, clinical and cytological work-up prior to surgical biopsy. In addition, 126 spiculated carcinomas detected in the same period were reviewed and compared. RESULTS: Fourteen RS/CSL (62%) had lucent centres and nine (38%) had a central mass; three had been diagnosed provisionally as RS/CSL. Spicule lengths ranged from 25 to 90 mm; central masses ranged from 5 to 50 mm; and mass:spicule length ratio ranged from 1.2:1 to 1:10. Calcification (benign or indeterminate) was present in six cases (29%). No RS/CSL contained 'suspicious' calcifications, whereas 120 of 126 carcinomas (95%) had a central mass and six (5%) had a lucent centre (spicule lengths: 10-90 mm; central mass: 5-40 mm; and mass:spicule length ratio: 1.1:1-1:10). Twenty-one spiculated carcinomas (17%) contained microcalcifications (14 benign or indeterminate; seven suspicious). Provisional radiological diagnosis (PRD) after mammogram, with or without ultrasound, for histologically confirmed RS/CSL, was RS/CSL in 18 cases (78%), carcinoma in four cases (17%) and equivocal in one case (5%). For eight (6.5%) spiculate carcinomas the PRD was RS/CSL prior to histological diagnosis. The RS/CSL were detected with equal frequency in right and left breasts, and 22 (96%) lesions occurred in the upper breast. Seven RS/CSL (31%) and 83 spiculated carcinomas (65%) had been described as 'palpable' but most were subtle. Twelve fine-needle aspiration biopsies were performed (six 'palpable' lesions (no radiological guidance); four with ultrasound guidance and two with stereotactic guidance), and five (62.5%) of eight adequate lesions were reported as benign, two (25%) were reported as atypical, and one (12.5%) was reported as suspicious. CONCLUSIONS: Definitive mammographic and sonographic differentiation of RS/CSL and stellate-type carcinoma is impossible. For screen-detected lesions that may be RS/CSL, the appropriate surgical procedure is a small but adequate biopsy using guidewire or other localization methods with optimal cosmetic incision.

HER2 testing recommendations in Australia.

HER2 is the target of a new treatment for metastatic breast cancer using the humanised monoclonal antibody trastuzumab (Herceptin). Since only around 20% of breast cancers carry the overexpressed HER2 receptor protein to which this treatment is directed, patient selection is very important in determining eligibility for the drug. Currently, immunohistochemistry and fluorescence in situ hybridisation are the main tests used for HER2 detection, and these testing recommendations have been developed based on national and international data.

Recent developments in stereotactic breast biopsy methodologies: an update for the surgical pathologist.

Recently, there have been a number of new devices introduced for stereotactic biopsy of nonpalpable, mammographically detected lesions. The vacuum-assisted core biopsy (VACB) (Minimal Invasive Breast Biopsy (MIBB), U.S. Surgical, Norwalk, CT; Mammotome, Biopsys Medical, Cincinnati, OH) obtains multiple tissue cores (11-gauge) in a circumferential manner around the biopsy probe, inserted under stereotactic guidance. It provides more complete sampling of mammographic lesions than the conventional 14-gauge stereotactic core biopsy, reducing the number of unsatisfactory biopsies. The advanced breast biopsy instrumentation (ABBI) (United States Surgical Corporation, Norwalk, CT) system utilizes stereotactic technique and an oscillating blade-cutting mechanism to obtain a single large diameter (5 mm to 20 mm) tissue core, with the aim of obtaining an intact lesion in its entirety for histologic assessment. Its potential as a treatment option is still under investigation. Suggested protocols for specimen handling are presented together with a review of the recent literature. Close liaison with radiologists and surgeons performing these biopsies will allow the collection of further outcome data to evaluate the strengths and weaknesses of each technique.

An audit of breast cancer pathology reporting in Australia in 1995.

To measure the quality of pathology reporting of breast cancer and establish a baseline against which future changes can be measured, we audited item completeness in breast cancer reports in Australia in 1995 before the release of specific recommendations from the Australian Cancer Network. Tumour type and size were given in reports of invasive breast cancer for 93% of women, 70% had, in addition, grade and clearance of the margins while only 28% had all recommended information. The most complete items in reports were histological type of breast cancer (99.6% of cases), tumour size (94%, 95% confidence interval (CI) 92-95) and margins of excision (87%, 95% CI 85-89). Histological grade (84%, 95% CI 82-86 of cases) and presence or absence of ductal carcinoma in situ (DCIS) (79%, 95% CI 77-81) were less complete and vessel invasion (61%, 95% CI 58-63) and changes in non-neoplastic breast tissue adjacent to the breast cancer (68%, 95% CI 66-71) the least complete. Less than half the reports of DCIS reported on tumour size (49%, 95% CI 42-57), presence or absence of necrosis (41%, 95% CI 34-49) or nuclear grade (39%, 95% CI 31-46). Around 1500 reports were identified as issued by 147 laboratories and 392 pathologists; 69% of pathologists issued fewer than two reports a month in the audit. We concluded that infrequency of reporting may have contributed to incompleteness of reporting. In addition, we found significant variation across Australian states with some indication that reporting was consistently poor in one state. The audit highlighted areas for improvement for breast cancer reporting in Australia. Research evidence suggests that multifaceted strategies are needed to assist practitioners with implementing more uniform reporting standards.

Conservative surgery and radiation therapy for invasive lobular carcinoma of the breast.

BACKGROUND: There is debate as to whether infiltrating lobular carcinoma (ILC) can be effectively treated with breast conservative surgery (CS) and radiotherapy (RT) because of a perceived high risk of local recurrence. This retrospective study examined the outcome of patients with ILC treated by CS and RT. METHODS: Between November 1979 and December 1994, 57 women with UICC Stage I or II ILC were treated by CS and RT at Westmead Hospital, New South Wales, Australia. The median age was 55 years (range 28-79). Twelve patients (21%) underwent a re-excision after initial CS. The final margins were clear for 43 patients (75.4%), positive (invasive or in situ) for nine patients (15.8%), and indeterminate for five patients (8.8%). All patients received whole-breast irradiation (45-50.4 Gy) usually supplemented by a boost (10-30 Gy). Fifty-three of 57 patients (93%) had their pathology reviewed at Westmead Hospital. RESULTS: After a median follow up of 69 months (range 36-162) three patients (5.3%) developed a local recurrence. One of 43 patients (2.3%) with known clear margins developed a local recurrence compared with two of 14 patients (14.3%) with positive or indeterminate margins (P = NS). The 5- and 10-year rates of freedom from local recurrence were 96 and 93%, respectively. The 5-year disease-free survival was 85% (node-negative, 92%; node-positive, 66%). Overall survival was 94% at 5 years. No patient developed a contralateral breast cancer. CONCLUSION: Patients with ILC can be effectively treated with CS and RT.

Is centralized histopathology review necessary for screen-detected breast lesions?

To address quality requirements for breast pathology in the Australian screening programme, one breast cancer Screening and Assessment Service initiated a process of central pathologic review of all lesions detected through the service. The aim of this study was to measure concordance between the initial and review pathology, and to assess the merit of routine review. Concordance was measured by observed agreement and the kappa statistic for 267 women with 273 lesions. Concordance was excellent for the four classification schemes examined, good for the identification of benign lesions and hyperplasia, and excellent for the identification of DCIS or invasive carcinoma. For the sub-categorization of hyperplasias and invasive carcinomas concordance was good, but was poor for the sub-typing of DCIS. Initial and review concordance was acceptable, suggesting that disagreement among pathologists may not present a major impediment to the provision of dependable diagnoses. Full case review is unnecessary for benign lesions or invasive carcinoma, but should be maintained for DCIS and hyperplasias.

Carcinomas of the renal pelvis associated with smoking and phenacetin abuse: p53 mutations and polymorphism of carcinogen-metabolising enzymes.

Phenacetin abuse and smoking are established risk factors for transitional cell carcinomas of the urinary tract. In the present study, we analysed exposure and the clinical course of patients who underwent nephrectomy for transitional cell carcinoma of the renal pelvis. PCR-SSCP of archival, paraffin-embedded histological sections followed by direct DNA sequencing revealed that 29 of 89 (33%) renal pelvic carcinomas contained a p53 mutation. Double mutations were found in 4 tumours and triple mutations in 1 tumour. The incidence of p53 mutations was significantly higher in tumours with grades 3 and 4 than in those with grades 1 and 2 and higher in invasive than in non-invasive tumours. Furthermore, patients with carcinomas carrying a p53 mutation showed poorer survival than those without mutation. The type of p53 mutation in renal pelvic carcinomas was similar to that reported for bladder cancer, G:C-->A:T transition mutations being most frequent (45%, 33% of these at CpG sites), followed by G:C-->T:A and G:C-->C:G transversions. The incidence and type of p53 mutation did not differ significantly in patients with a history of phenacetin abuse, smoking or neither of these habits. This was also true for G:C-->T:A transversions (17.5% of mutations), which are considered typical of smoking-induced carcinomas at other sites, e.g., lung, oral cavity and oesophagus. Our results indicate that the frequency and pattern of p53 mutations are similar in transitional cell carcinomas of the bladder and the renal pelvis and do not reflect exposure to phenacetin and/or smoking. The frequency of genetic polymorphism in genes coding for carcinogen-metabolising enzymes (CYP1A1, NAT1, GSTT1 and GSTM1) was also independent of exposure. Although the sample size of our study does not allow definite conclusions, these data are compatible with chronic tissue damage as a causative factor in the evolution of urothelial carcinomas rather than pointing to a direct mutagenic effect of phenacetin and tobacco-specific carcinogens.