Prescription drug screening for subsequent carcinogenicity

Drug-Wide Association Study (DWAS): Challenges and Opportunities

Cancer risk associations with commonly prescribed medications have been mainly evaluated in hypothesis-driven studies that focus on one drug at a time. Agnostic drug-wide association studies (DWAS) offer an alternative approach to simultaneously evaluate associations between a large number of drugs with one or more cancers using large-scale electronic health records. Although cancer DWAS approaches are promising, a number of challenges limit their applicability. This includes the high likelihood of false positivity; lack of biological considerations; and methodological shortcomings, such as inability to tightly control for confounders. As such, the value of DWAS is currently restricted to hypothesis generation with detected signals needing further evaluation. In this commentary, we discuss those challenges in more detail and summarize the approaches to overcome them by using published cancer DWAS studies, including the accompanied article by Støer and colleagues. Despite current concerns, DWAS future is filled with opportunities for developing innovative analytic methods and techniques that incorporate pharmacology, epidemiology, cancer biology, and genetics.See related article by Støer et al., p. 682.

A systematic assessment of the association between frequently prescribed medicines and the risk of common cancers: a series of nested case-control studies

BACKGROUND

Studies systematically screening medications have successfully identified prescription medicines associated with cancer risk. However, adjustment for confounding factors in these studies has been limited. We therefore investigated the association between frequently prescribed medicines and the risk of common cancers adjusting for a range of confounders.

METHODS

A series of nested case-control studies were undertaken using the Primary Care Clinical Informatics Unit Research (PCCIUR) database containing general practice (GP) records from Scotland. Cancer cases at 22 cancer sites, diagnosed between 1999 and 2011, were identified from GP records and matched with up to five controls (based on age, gender, GP practice and date of registration). Odds ratios (OR) and 95% confidence intervals (CI) comparing any versus no prescriptions for each of the most commonly prescribed medicines, identified from prescription records, were calculated using conditional logistic regression, adjusting for comorbidities. Additional analyses adjusted for smoking use. An association was considered a signal based upon the magnitude of its adjusted OR, p-value and evidence of an exposure-response relationship. Supplementary analyses were undertaken comparing 6 or more prescriptions versus less than 6 for each medicine.

RESULTS

Overall, 62,109 cases and 276,580 controls were included in the analyses and a total of 5622 medication-cancer associations were studied across the 22 cancer sites. After adjusting for comorbidities 2060 medicine-cancer associations for any prescription had adjusted ORs greater than 1.25 (or less than 0.8), 214 had a corresponding p-value less than or equal to 0.01 and 118 had evidence of an exposure-dose relationship hence meeting the criteria for a signal. Seventy-seven signals were identified after additionally adjusting for smoking. Based upon an exposure of 6 or more prescriptions, there were 118 signals after adjusting for comorbidities and 82 after additionally adjusting for smoking.

CONCLUSIONS

In this study a number of novel associations between medicine and cancer were identified which require further clinical and epidemiological investigation. The majority of medicines were not associated with an altered cancer risk and many identified signals reflected known associations between medicine and cancer.

A novel two-stage, transdisciplinary study identifies digoxin as a possible drug for prostate cancer treatment

Identification of novel indications for commonly prescribed drugs could accelerate translation of therapies. We investigated whether any clinically-used drugs might have utility for treating prostate cancer by coupling an efficient, high-throughput laboratory-based screen and a large, prospective cohort study. In stage 1, we conducted an in vitro prostate cancer cell cytotoxicity screen of 3,187 compounds. Digoxin emerged as the leading candidate given its potency in inhibiting proliferation in vitro (mean IC₅₀=163 nM) and common use. In stage 2, we evaluated the association between the leading candidate drug from stage 1 and prostate cancer risk in 47,884 men followed 1986-2006. Regular digoxin users (versus nonusers: RR=0.76, 95% CI 0.61-0.95), especially users for ≥ 10 years (RR=0.54, 95% CI 0.37-0.79, P-trend<0.001), had a lower prostate cancer risk. Digoxin was highly potent in inhibiting prostate cancer cell growth in vitro and its use was associated with a 25% lower prostate cancer risk.

SIGNIFICANCE

Our two-stage transdisciplinary approach for drug repositioning provides compelling justification for further mechanistic and possibly clinical testing of the leading nonchemotherapy candidate, digoxin, a cardiac glycoside, as a drug for prostate cancer treatment. Perhaps of equal importance, our study illustrates the power of the transdisciplinary approach in translational cancer research. By coupling laboratory and epidemiologic methods and thinking, we reduced the probability of identifying false-positive candidate drugs for the next steps in testing.

Screening pharmaceuticals for possible carcinogenic effects: initial positive results for drugs not previously screened

OBJECTIVE

To screen commonly used prescription drugs for possible carcinogenic effects.

METHODS

In a large health care program we identified 105 commonly used drugs, not previously screened. Recipients were followed for up to 12½ years for incident cancer. Nested case-control analyses of 55 cancer sites and all combined included up to ten matched controls per case, with lag of at least 2 years between drug dispensing and cancer. Positive associations entailed a relative risk of 1.50, with p ≤ 0.01 and higher risk for three or more, than for one prescription. Evaluation included further analyses, searches of the literature, and clinical judgment.

RESULTS

There were 101 associations of interest for 61 drugs. Sixty-six associations were judged to have involved substantial confounding. We found evidence that of the remaining 35, the following associations may not be due to chance: sulindac with gallbladder cancer and leukemia, hyoscyamine with nonHodgkin lymphoma, nortriptyline with esophageal and hepatic cancer, oxazepam with lung cancer, both fluoxetine and paroxetine with testicular cancer, hydrochlorothiazide with renal and lip cancer, and nifedipine with lip cancer.

CONCLUSIONS

These preliminary findings suggest that further studies are indicated regarding sulindac, hyoscyamine, nortriptyline, oxazepam, fluoxetine, paroxetine, hydrochlorothiazide, and nifedipine.

Epidemiologic evaluation of pharmaceuticals with limited evidence of carcinogenicity

Thorough review by the International Agency for Research on Cancer (IARC) has resulted in classifying many substances, including pharmaceuticals, as probably or possibly carcinogenic to humans, based on experiments on animals or limited data on humans. We evaluated 9 such pharmaceuticals for evidence of carcinogenicity in patients receiving them in a large medical care program with automated pharmacy records and a cancer registry. Nested case-control analyses were performed in a cohort of 6.5 million subscribers with up to 12 years of follow-up, focusing on cancer sites suggested by previous evidence and other sites with odds ratio of at least 1.50, p < 0.01 and some evidence of dose-response. Unmeasured confounding was estimated in sensitivity analyses. We found some supportive evidence for carcinogenicity of griseofulvin, metronidazole and phenytoin and for the known carcinogen, cyclophosphamide, which was added for validation of our data and analyses. Findings for chloramphenicol, iron-dextran complex, phenoxybenzamine and phenobarbital were essentially non-contributory. Confounding by cigarette smoking and prior thyroid disease could account, respectively, for associations of oxazepam with lung cancer and propylthiouracil with thyroid cancer. Although not definitive, these findings should be considered in the evaluations of these pharmaceuticals.

Pharmaceuticals that cause mammary gland tumors in animals: findings in women

Risk of breast cancer in women was assessed for eight pharmaceuticals that produce mammary tumors in experimental animals, using nested case-control analyses in two cohorts with prescription records in a comprehensive medical care program. The two cohorts were: (1) earlier cohort: 78,118 female members who received prescriptions in 1969-1973, of whom 2,467 developed breast cancer, and (2) later cohort: 3,289,408 female members who received prescriptions in 1994-2006 of whom 24,528 developed breast cancer. Longest follow-up was until June 30, 2006. Ten randomly selected concurrent control women were age-matched to almost every case. Relative risks were estimated by conditional logistic regression. Case ascertainment was lagged by 2 years, or unlagged and subdivided by number of prescriptions received. Some analyses were controlled for hormone use and sensitivity analyses were conducted to estimate the effects of uncontrolled confounding. In the later cohort furosemide, and metronidazole showed statistically significant but very small increases in relative risk (ranging from 1.07 to 1.13). Of these, only furosemide showed increased risk in the earlier cohort: 2-year lag relative risk 1.66 (95% confidence interval 1.23-2.24) or as low as 0.97, assuming uncontrolled positive confounding. Griseofulvin showed significant increases in the later cohort: relative risk for three or more prescriptions 1.48 (1.08-2.03) or as low as 1.23 assuming uncontrolled positive confounding and non-significant increases were noted in the earlier cohort. Our findings are limited by their inconsistency across the two cohorts and our inability to directly control for most established breast cancer risk factors. Although inconclusive, our findings suggest a need for more research on furosemide and griseofulvin.

Antibiotics and Risk of Breast Cancer: Up to 9 Years of Follow-up of 2.1 Million Women

Antibiotic use has been associated with risk of breast cancer in previous reports. Using Cox proportional hazards analysis, we evaluated this association in 2,130,829 adult female subscribers of a health care program according to their receipt of prescriptions of antibiotics from outpatient pharmacies. Hormone use was taken into account. Altogether, 18,521 women developed breast cancer in up to 9.4 years of follow-up. Use of any antibiotic was associated with slightly increased risk [hazard ratio (HR), 1.14; 95% confidence interval (95% CI), 1.10-1.18] but there was little, if any, evidence of dose response, with HR of 1.17 (95% CI, 0.97-1.42) for >1,000 days of use compared with no use. The only two weakly associated antibiotic groups (HR >1.10 for >100 days of use) were tetracyclines and macrolides with HRs (95% CI) of 1.23 (1.11-1.36) and 1.16 (0.98-1.36), respectively. An association of lincosamides with breast cancer in an earlier, smaller database was not confirmed, but follow-up was too short in the present data for adequate evaluation. Medical record review suggested that acne and/or rosacea could be the underlying factor, associated with long-term antibiotic therapy and found by others to be associated with risk of breast cancer. Although causality cannot be ruled out, the observed associations of antibiotics overall, tetracyclines, and macrolides with breast cancer were weak and could be explained by uncontrolled confounding by the diseases being treated or by other factors.

Breast Cancer Risk Among Users of Antidepressant Medications

BACKGROUND

Breast cancer is the most common cancer in women. Laboratory studies suggest that antidepressants may promote breast cancer tumor growth. Several epidemiologic studies have evaluated this association with conflicting results.

METHODS

We conducted a cohort study with a secondary nested case-control analysis based on the General Practice Research Database. Our goal was to assess the association between the risk of breast cancer and use of serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and other antidepressants. We calculated adjusted estimates controlling for breast cancer risk factors using unconditional logistic regression.

RESULTS

A total of 3708 cases of breast cancer were ascertained. Overall, antidepressant use was not associated with an increased risk of breast cancer. Current users of SSRIs had an odds ratio (OR) of 0.98 (95% confidence interval=0.81-1.19), whereas current users of TCAs had an OR of 0.86 (0.73-1.00). When only use for longer than 1 year was considered, the corresponding estimates for SSRIs and TCAs were 0.76 (0.53-1.09) and 0.87 (0.70-1.09), respectively. None of the individual drugs was associated with breast cancer risk.

CONCLUSIONS

Use of antidepressants was not associated with an increased risk of breast cancer regardless of duration of use, daily dose, or specific drug being used. These results, together with evidence from prior studies, support the lack of a clinically meaningful association between breast cancer risk and antidepressants.