Evaluation of therapy with methanol extraction residue of BCG (MER)

The current status of therapy with the methanol extraction residue of BCG (MER) is reviewed. We have identified 41 evaluable clinical trials of MER therapy, involving approximately 3,000 patients with malignant disease. The diagnoses have included lung, colon, and breast cancer, malignant melanoma, acute leukemia, and a small number of other malignancies. MER has been used as an adjunct to therapy for advanced disease and as prophylaxis against recurrence after surgery. Most studies have used the intradermal route but subcutaneous, intralesional, and intravenous routes have also been explored. The major local toxicity is pain and sterile abscess formation. The major systemic toxicity with administration by the intravenous route includes fever, malaise, and the development of pulmonary infiltrates. With the intradermal route little activity has been observed and there is no confirmed example of an increased remission rate, remission duration, or survival induced by MER therapy. When given by the intralesional route MER can cause regression of metastatic malignant melanoma nodules, and when given by the intravenous route MER is a potent immunoadjuvant. Antibody-dependent cellular cytotoxicity and natural killer cell activity were both boosted after one dose of intravenous MER. In rare patients receiving either intradermal or intravenous MER alone, without other therapy, tumor regression has been noted. These cases have included gastrointestinal cancer, lymphoma, and leukemia. Overall, the data indicate that the future of therapy with mycobacterial fractions awaits the development of more potent, less toxic fractions that can be administered systemically.