Type B lactic acidosis is thought to be a rare complication of malignancy. It was first described in patients with acute leukaemia by Field et al. in 1963. Since then, it has been observed more often, in particular in haematological malignancies and rarely in solid tumours. Previously reported cases of lactic acidosis in solid malignancy are reviewed. In addition, we report a case of type B lactic acidosis in a woman with metastatic breast cancer. Afterwards, we speculate on the elusive pathophysiology of this oncological emergency. 14 cases of lactic acidosis due to solid malignancies, without prior chemotherapy, were identified. The cases were published from the year 1978 to 2006. Several theories concerning the mechanism for type B lactic acidosis in solid malignancy have been postulated. During the last decade, more and more evidence supports the role of overproduction of lactic acid due to ischaemia in the neoplastic tissue bed and with cancer cells having an aberrant energy production.