The growth rate of bone sarcomas and survival after radiotherapy with tourniquet-induced hypoxia: a clinical study

Quantitative analysis of tumor growth rate and changes in tumor marker level: specific growth rate versus doubling time

BACKGROUND

Doubling time (DT) of tumor volume has been widely used to estimate the growth rate of tumors. However, DT gives incorrect estimates of the average growth rate of tumors when the uncertainty of growth rate is considerable. Specific growth rate (SGR) is less affected by uncertainties and is a more relevant parameter. Optimized imaging techniques and prolonged interval between observations can reduce the uncertainty of growth rate estimation. DT is also used for defining changes in tumor marker level. The aim of this study was to compare DT and SGR as measures of growth rate when the uncertainty is negligible.

METHODS

Mathematical analysis and computer simulations were carried out assuming no uncertainty of growth rate estimation. Data from two previously published clinical studies were assessed by both variables.

RESULTS

Due to the non-linear relationship between DT and SGR, using these variables does not give similar results. The variation of DT is not uniformly indicating variations of the growth rate. DT largely overestimates the difference in growth rate of slowly growing tumors and underestimates the difference in growth rate of rapidly growing tumors. On the other hand, SGR uniformly indicates the difference between growth rates throughout all ranges. Quantitative analysis of clinical observations can lead to contradictory results depending on the variable used for growth rate.

CONCLUSION

The growth rate of tumor volume should be expressed by SGR, or percentage increase per unit time, regardless of the level of the uncertainty of growth rate estimation. This conclusion is also valid for changes in tumor marker level, whether it is correlated with the growth rate of tumor volume or not.

Specific growth rate versus doubling time for quantitative characterization of tumor growth rate

Doubling time (DT) is widely used for quantification of tumor growth rate. DT is usually determined from two volume estimations with measurement time intervals comparable with or shorter than DT. Clinical data show that the frequency distribution of DT in patients is positively skewed, with some very long DT values compared with the average DT. Growth rate can also be quantified using specific growth rate (SGR; %/d), equal to ln2/DT. The aim of this work was to compare DT and SGR as growth rate variables. Growth rate calculations were computer simulated for a tumor with DT of 100 days, measurement time interval of 1 to 200 days, and volume estimation uncertainty of 5% to 20%. Growth rate variables were determined and compared for previously published clinical data. The study showed that DT is not a suitable variable for tumor growth rate because (a) for short measurement time intervals, or high volume uncertainties, mean DT can either overestimate or underestimate the average growth rate; (b) DT is not defined if the consecutively estimated volumes are equal; and (c) the asymmetrical frequency distribution of DT makes it unsuitable for common statistical testing. In contrast, mean SGR and its equivalent DT give the correct values for average growth rate, SGR is defined for all tumor volume changes, and it has a symmetrical frequency distribution. SGR is also more accurate to use when discussing, for example, growth fraction, cell loss rate, and growth rate heterogeneities within the tumor. SGR should thus be used, instead of DT, to quantify tumor growth rate.

Intra-arterial cisplatin with or without radiation in limb-sparing for canine osteosarcoma

METHODS

Forty-nine dogs with spontaneously occurring osteosarcoma underwent limb-sparing surgery after preoperative therapy consisting of intra-arterial cisplatin alone or intra-arterial cisplatin in combination with doses of radiation from 20-40 Gy in 10 fractions. All resections were marginal, and the defect was repaired with a cortical allograft.

RESULTS

Local tumor control was strongly influenced by the percent necrosis in the excised specimen. Overall, the estimated 1-year local recurrence rate was approximately 32% (by life-table estimate). Dogs with less than 75% necrosis had an estimated 1-year recurrence rate of 65%; those with greater than 75% necrosis had an estimated 1-year recurrence rate of 15% (P = 0.004, by log-rank test). Local recurrence was influenced by the radiation dose. Dogs receiving 28 Gy or less had an estimated 50% 1-year recurrence rate, and those receiving 32 Gy or more had an estimated 8% 1-year recurrence rate (P = 0.03, by log-rank test). Normal host bone more frequently became necrotic at doses of 36 Gy or more.

CONCLUSIONS

Intra-arterial cisplatin in combination with moderate doses of radiation (32 Gy) can achieve a high percent tumor necrosis while maintaining host bone viability. Survival was limited by distant metastasis but was lengthened by treatment compared with some earlier findings.

Limb salvage surgery for bone and soft tissue sarcoma. A phase II pathologic study of preoperative intraarterial cisplatin

Preoperative therapy has been tested as part of limb salvage therapy for localized bone and soft tissue sarcoma of the extremities. The activity of cisplatin (CDDP) by intraarterial (IA) infusion was evaluated in 40 cases of which 36 were evaluable for response. All patients had high-grade sarcomas. All but 3 patients received 3 or 4 courses (24 patients received 4 courses) of CDDP at a dosage of 120 to 150 mg/m2 given over 6 hours every 2 weeks by IA infusion. Patients younger than 18 years of age received the higher dose of CDDP. Treatment was well tolerated with combination antiemetics. One patient experienced severe hearing loss with the first cycle of the higher CDDP dose. Pathologic evaluation of resected osteosarcoma showed a favorable response (90% or greater necrosis) in 8 of 20 evaluable cases and in 3 of 4 patients with malignant fibrous histiocytoma (MFH) of bone (without osteoid). In soft tissue sarcomas, minimal (50% to 89%) necrosis was seen in two of nine cases and none had 90% or greater necrosis. Patients received postoperative chemotherapy based on pathologic response, but the value of this postoperative adjuvant therapy requires further follow-up and is uncertain in this small study. IA CDDP can often cause significant tumor necrosis in patients with bone sarcomas, whereas soft tissue sarcomas are less sensitive to this therapy.

Advances in hypoxyradiotherapy

Observations in animal experiments and in Phase I clinical trials on the effect of breathing 8-10% oxygen are summarized. The animal tests indicated that the hypoxia induced in this way for periods varying between 10-45 minutes had a radioprotective effect on normal tissues. Patients tolerated the hypoxic treatment given for 15 minutes without any acute or late complications. Phase II trials have been started to test the effect of hypoxic radiotherapy in administering a larger total tumor dose than in conventional radiotherapy.