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Centre for Evidence-
Based Medicine

Completed Diagnosis Worksheet for Evidence-Based General Surgery

Citation

Drew PJ, Kerin MJ, Turnbull LW, Imrie M, Carleton PJ, Fox JN & Monson JRT. Routine screening for local recurrence following breast-conserving therapy for cancer with dynamic contrast-enhanced magnetic resonance imaging of the breast. Ann Surg Oncol 1998;5:265-70

Are the results of this diagnostic study valid?

  1. Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
    Yes. The standard used (mammography plus palpation, but without routine use of ultrasound) could be criticised as suboptimal, but is representative of contemporary specialist practice in the UK.
  2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)?
    Probably. The new test (MRI) was offered to women undergoing breast-conserving therapy. The paper does not mention any exclusions, and it does not say how many women refused to take part, nor whether they were different from those who participated.
  3. Was the reference standard applied regardless of the result of the new diagnostic test?
    Yes

Are the valid results of this diagnostic study important?

Outcome
MRI Result Cancer Benign Likelihood Ratio
Positive 9/9 6/96 16*
Negative 0/9 90/96 0

Can I apply this valid, important evidence about a diagnostic test in caring for my patient?

  1. Is the diagnostic test available, affordable, accurate and precise in my setting?
    Is the diagnostic test available, affordable, accurate and precise in my setting?
  2. Can I generate a clinically sensible estimate of my patient's pre-test probability of having local recurrence?
    The scenario suggests that there is enough clinical thickening to raise concern, but no convincing features of recurrence. From experience, I would guess at a pretest probability of cancer of maybe 20% in this situation.
  3. Will the resulting post-test probabilities affect my management and help the patient?
    The pre-test odds are 1:5, x the LR of 16 = post test odds of 16:5 or 3.2:1. This is equivalent to a post-test probability of having recurrent cancer of 76% if the MRI is positive: this would certainly be enough to recommend biopsy.
  4. Would the consequences of the test help my patient?
    Yes, provided she was not so determined to avoid surgery that nothing could sway her.

Clinical Bottom Line

This looks like a considerable advance for the diagnosis of local recurrence after breast conserving surgery. We need to be sure that it can be done everywhere, not just by one group of experts.

Additional Notes

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