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October 1990, Volume 40, Issue 10

Case Reports

MEGA DOSES OF METHOTREXATE IN THE TREATMENT OF OSTEOSARCOMA

M. Perwaiz Iqbal  ( Departments of Biochemistry, The Aga Khan University Medical College, Karachi. )
Imtiaz A. Malik  ( Departments of Medicine, The Aga Khan University Medical College, Karachi. )

High-dose-methotrexate therapy with eitrovorum factor (leucovorin) rescue has been widely used in the treatment of many solid tumors and lymphomas. This therapy plays an important role in the management of osteosarcoma1-7. The rationale behind using high doses of this drug is to achieve high plasma levels (10 to 10-5 M)for prolonged periods8. This probably facilitates the passive entry of methotrexate (MTX) into the tumor cells having defective transport systems9. It has also been suggested that increased intracellular levels of free MTX can over come drug resistance caused by increased levels of dihydrofolate reductase (DHFR) or presence of a DHFR having low affinity for MTX10 Moreover, such high doses facilitate MTX polyglutamate formation within the tumor cells and hence prolong its cytotoxie effects11. On these basis, such therapy has been advocated for base in osteosar­coma1,2,6,7. The treatment has been shown to reduce regression of primary and metastatic tumors12-16 and response rates seem to increase with more frequent and intense treatments14,17. More recently, some workers have used 12 g/m2 of MTX which results in improved response rate and survival18. Previously we have reported the treatment of two cases of metastatic osteosarcoma with high doses (5 g/m2) of MTX19. Mega doses, however, have not been attempted in Pakistan due to its prohibitive cost and toxicity. We recently treated a case of osteosarcoma with 12 g/m2 of MTX on four different occasions. We monitored the MTX levels in the plasma as well as RBCs and evaluated the toxicity and clinical outcome of this patient.

CASE REPORT

A twenty six year old male was admitted to the Aga Khan University Hospital in November, 1988 with a history of right knee pain and later swelling of the lower end of femur. Radiologic examination revealed an osteolytic lesion in the lower end of femur. A bone biopsy done in late October showed a tumour composed of neoplastic cells with pleoniorphic, hyperchromatic nuclei, osteoid forma­tion, foci of calcification, scattered giant cells and areas of necrosis. He was diagnosed to have osteosarcoma. His physical examination, except for above knee swelling, was normal. Metastatic work-up including ultrasound liver and CT scan of chest was normal. Laboratory studies including CBC, electrolytes, BUN and creatinine were normal. He was started on Rosen’s T-10 protocol20. Prior to chemotherapy, patient received hydration and alkaliniza­tion of urine with NaHCO3 to keep the urine pH > 7.0. Chemotherapy was carried out as shown in Figure 1.

MTX was administered as a continuous infusion over six hours. Blood sampling was done at regular intervals to monitor MTX levels. Leucovorin rescue at 15 mg/m2 was started 24-hours after MTX infusion every six hours until MTX level fell to <1.0 X 10-7 M.MTX concentration in plasma and erythrocytes was determined by a very sensitive radioassay21. Erythrocytes were first washed with saline and thea hemolysed in three volumes of deionized water and the proteins precipitated by placing the hemolysate in a boiling water bath for 5 minutes. This exti-action proce­dure of the drug from erythrocytes has been described elsewhere22. Profiles of MTX levels from plasma and erythrocytes after a six hour infusion of MTX are shown in Figures 2 and 3.


Figure 2 shows that following all the four courses of MTX, the plasma levels of MTX during the first 12 hours following the completion of infusion remained within the range of 10-4 to 10-5 M. This is the concentration that has been shown to facilitate passive diffusion of the drug into the tumor cells or entry of the drug by a low affinity, high capacity carrier system9. Erythrocytes MTX profile during these 4 courses is shown in Figure 3. In all the infusions, there was substantial entry of the drug (> 104 M) into erythrocytes probably by simple diffusion as well as by carrier system22. However, subsequent to the first infusion, MTX levels in erythro­cytes were found to be greater than 10-7 M at various time intervals. These higher levels are partly contributed by newly formed red cells. At notime during the course of treatment did the patient exhibit any symptoms of moderate or severe clinical toxicity. Mild nausea and vomiting were the only complaints. Renal toxicity was effectively prevented by hydration and urinary alkalinization23. Leucovorin rescue at 15mg/m2 every 6 hours was continued until MTX levels fell below 1.0 x 10-7 M. This effectively prevented hematologic and mucosal toxicity. Moreover at 48 hours post- infusion, MTX levels in plasma were well below 10-6M (Figure 2). Levels above 10-6 M at 48 hours are directly related to severe toxic effects19,23-25. Patient received three courses of MTX at 12 Wm2 one week apart, followed one week later by chemotherapy with bleomycin, cyclophosphamide and actinomycin-D. Three weeks later, he received fourth course of MTX (12 g/m2). At the end of the fourth course of MTX, he had achieved significant tumor regression. He underwent amputation in February 1989. Since thenhe has been continued onT-lO protocol and till today, remains disease free.

DISCUSSION

During the past several years, there has been a significant improvement in the disease-free survival of patients with osteosarcoma. Although it has been mostly attributed to the use of adjuvant chemotherapy, con­troversy remained as to the precise role played by chemotherapy. Some studies clearly showed better out­come with the use of chemotherapy2,5-7, others maintained that the natural history of the disease has changed to that of a better prognosis with surgery alone26. Regarding the studies that failed to show the efficacy of the adjuvant chemotherapy, the poor response was attributed to the use of chemotherapy, the poor response was attributed to the use of sub-optimal doses of MTX7. More recently, two large multi-institutional studies have clearly established the role of chematherapy in the management of osteosar­coma27,28.  MTX at 12 g/m2 plays a central role in the drug combinations used in the management of osteosar­coma6,18,20,27,28. These high doses have been suggested to increase passive diffusion into the tumour cells and overcome drug resistance caused by amplification of DHFR qene as well as the induction of a low-affinity DHFR9,10. This therapy, however, can be extremely toxic. Major toxicity is severe mucositis, bone-marrow suppres­sion and azotemia. Utilizing proper precautionary measures, such as hydration and alkalinization of urine to decrease MTX precipitation in the renal tubules and leucovorin rescue to prevent bone marrow suppression, this treatment can safely be given. Indeed, in our patient no clinical toxicitywas observed. CBC, electrolytes, BUN and creatinine were repeatedly measured and remained within normal limits. The MTX plasma levels achieved were clearly in a range (10-4 to 10-5M) that is associated with enhanced passive diffusion of drug into the tumor cells. Erythrocytes MTX levels also were indicative of substantial entry of drug into the RBC\'s. After the first infusion, these levels were found to be greater than 10-7 M at different time intervals. These higher levels are partly contributed by the MTX that got incorporated into the red cell precursors in the bone marrow during the earlier infusions since RBC’s take 5-7 days to mature and enter the circulation22. The efflux of MTX from the red cells as the plasma concentra­tion decreases may serve to deliver supplementary amount of the drug to the tissues. Since tumor tissue in osteosarcoma has been shown to accumulate more drug than the surrounding normal tissue, this may account for enhanced cytotoxic effect on the tumour cells while sparing the normal tissue5,29.  The clinical response in this patient is most encouraging. Twenty years ago, these patients had more than 80% chance of developing metastatic disease30. With the protocols similar to the one used here, prognosis has improved to a disease-free survival of over 70% at 5 years31-33. This patient remains disease free at 18 months of follow-up.

ACKNOWLEDGEMENTFS

We gratefully acknowledge the technical help of Ms. Naseema Mehboobali in conducting the MTX assays. We also appreciate the useful suggestions and support of Professor M. Anwar Waqar.

REFERENCES

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