Sunday, April 29, 2012

Sobrediagnòstic

Overdiagnosis of Invasive Breast Cancer Due to Mammography Screening: Results From the Norwegian Screening Program

En tota decisió clínica sabem que hi ha una probabilitat de falsos positius. També sabem que pot haver-hi sobrediagnòstic. El sobrediagnòstic és sovint confós amb el terme fals positiu d'una prova, però són dos conceptes diferents. Un resultat fals positiu d'una prova es refereix a una exploració complementària que suggereix la presència de la malaltia, però es tracta d'un error que es pot corregir amb una repetició de la prova. Als pacients sobrediagnosticats se'ls diu que tenen la malaltia i en general reben tractament. Els cas dels pacients sobrediagnosticats esdevé especialment preocupant. La seva magnitud és desconeguda però hi ha àrees on se sap més que altres.
Així per exemple llegint Annals podem saber que a Noruega i fruit dels programes de cribratge de càncer de mama han sobrediagnosticat entre un 15 i un 25% dels casos. Aquest és el resum:
A total of 39 888 patients with invasive breast cancer were included, 7793 of whom were diagnosed after the screening program started. The estimated rate of overdiagnosis attributable to the program was 18% to 25% (P < 0.001) for approach 1 and 15% to 20% (P < 0.001) for approach 2. Thus, 15% to 25% of cases of cancer are overdiagnosed, translating to 6 to 10 women overdiagnosed for every 2500 women invited.
Al llibre Overdiagnosed, quan es parla dels programes de cribratge de cancer de mama, s'assenyala:
If there were no overdiagnosis, then the total number of individuals diagnosed with cancer would be unaffected by screening. A rise in the number of breast cancers following the initiation of screening is expected (some people do have cancers destined to appear later that can be detected by screening),20 but if there is truly no overdiagnosis, that rise will be offset by reductions in the numbers of cancers detected later. In other words, if all cancers detected early through screening were ultimately going to be clinically evident (typically when a woman notices a new breast lump and then seeks medical care to evaluate it), one would expect a subsequent decline in the number of cancers detected clinically later in time. Since the cancers would have been detected and treated in women of screening age, the reduction should become evident as the women age and stop screening (in Europe, generally around ages sixty-five to seventy). Throughout Europe this reduction has largely failed to appear.
I assenyala que el problema del sobrediagnòstic és el sobretractament i cita la revisió Cochrane:
“The evidence review suggests that for every 2000 women invited to screening for 10 years one death from breast cancer will be avoided but that 10 healthy women will be overdiagnosed with cancer. This overdiagnosis is estimated to result in six extra tumorectomies and four extra mastectomies and in 200 women risking significant psychological harm relating to the anxiety triggered by the further investigation of mammographic abnormalities.”
Tema preocupant al que prestem una atenció limitada. A més de l'impacte en salut i benestar, hi ha l'impacte econòmic del qual desconeixem el seu abast a dia d'avui.

PS. Per a Catalunya cal consultar aquest article. L'estimació del sobrediagnòstic pot assolir fins i tot el 46%. Aquests són els resultats:
Incidence of invasive BC increased, especially in cohorts born from 1940 to 1955. The biggest increase was observed in these cohorts between the ages of 50 to 65 years, where the final BC incidence rates more than doubled the initial ones. Dissemination of mammography was significantly associated with BC incidence and overdiagnosis. Our estimates of overdiagnosis ranged from 0.4% to 46.6%, for women born around 1935 and 1950, respectively.

A l'exposició de Chagall el podreu veure fins el 20 de maig, després se l'endurà la duquessa.

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