Predicting lymph node involvement in cases of delay in diagnosis of breast cancer

20 June 2013

By Sarah Vallance, Medical Law Department, Brisbane

When a woman is diagnosed with breast cancer, it can be difficult to predict that individual's response to treatment and their long-term prognosis. There are several systems of classification that attempt to predict the course of the disease using various prognostic factors, such as the size of the primary tumour, lymph node involvement, grading and hormone receptor status. However, even in a group of patients with similar types of breast cancer, the response to standard treatments varies.

When there has been a delay in diagnosis which leads to litigation, one of the greatest difficulties is proving what position the plaintiff would have been in if there had been a timely diagnosis of their cancer. This requires estimates to be made of any change in prognosis over the period of delay based on the extent of disease found when the cancer is detected. While the grade and hormone receptor status does not change over time, the size of the tumour and the risk of spread to the axillary lymph nodes do increase. If there has been a delay in diagnosis and there is lymph node involvement when the cancer is diagnosed, one of the critical issues will be determining when the cancer spread to the lymph nodes. There is no precise method to determine this. However, experts will be asked to express their opinion as to whether, on the balance of probabilities, there would have been lymph node involvement when the cancer should have been diagnosed.

These issues were recently debated in a case that Maurice Blackburn successfully acted in after a general surgeon in Queensland failed to investigate the cause of a woman's breast symptoms. In that case, the woman, a mother of three children, consulted the general surgeon in February 2009 after noticing bloody discharge from her left nipple. On examination, the surgeon noted a 1cm lump in the left breast. He did not arrange any further investigations, including a fine needle or core biopsy of the breast lump. Due to ongoing symptoms, further investigations were arranged, which led to a diagnosis of breast cancer in July 2009. By this stage, there was a 'large firm mass' in the plaintiff's left breast. No measurement of the mass was recorded. The plaintiff subsequently underwent a double mastectomy, chemotherapy, radiotherapy and Herceptin treatment. In March 2012, it was discovered the cancer had spread to the woman's liver. She has a very poor prognosis.

One of the central issues in dispute was whether the cancer had spread to the lymph nodes by February 2009. At diagnosis, two lymph nodes were involved with cancer and there was extensive disease in the left breast. The delay in diagnosis was relatively short. However, there had been a substantial increase in the size of the breast lump between February and July 2009. It was also notable that the woman had been breastfeeding, which can increase the rate of spread to the lymph nodes. If there had been lymph node involvement in February 2009, the treatment required and long-term prognosis would have been essentially the same and the value of the claim would have been extremely low.

The plaintiff's and defendant's experts both determined the probability of lymph node spread in the axilla at a point in time by using the equation "P (probability of lymph node spread) = diameter of tumour in mm + 15". One of the shortcomings in using this equation was that in February 2009 there was a clinical measurement but no pathological measurement, whereas in July 2009 there was no clinical measurement recorded but pathologically, the tumour measured 50 x 30 x 150mm (ductal carcinoma in situ and invasive cancer). There was dispute between the experts as to whether the diameter of the tumour should include the whole of the DCIS, or the largest deposit of invasive cancer within the DCIS, or the aggregate of invasive cancer within the DCIS. The plaintiff's expert used the diameter of the whole mass whereas the defendant's expert used the diameter of the largest deposit of invasive cancer.

The probability of lymph node spread in February 2009 when the tumour measured 1cm was estimated by applying Bayes theorem. Due to the different measurements used by the experts, one expert estimated there was a 15 per cent chance of lymph node involvement in February 2009 whereas the other expert estimated there was a 71 per cent chance of lymph node involvement.

This case demonstrates that there must be a significant difference in tumour size to prove, on the balance of probabilities, there was no lymph node involvement at the earlier date. In most cases, there has to be a delay in diagnosis of at least six to 12 months before the tumour will have increased enough in size to prove there was no lymph node involvement at the earlier date. However, it is possible to succeed in cases where there has been a shorter delay if there has been a significant increase in the size of the tumour during that period of delay.

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