Abstract P5-15-09: Evaluation of growth modulation index as a marker of benefit for consecutive lines of treatment for metastatic breast cancer
Authors: Ayala de la Peña F , Ivars Rubio A , de la Morena Barrio P , Fernández Sánchez A , Luengo Gil G , García Martínez E , García Garre E , Marín Zafra G , Vicente V 
Published: March 2017

Background: Sequencing of single-agent chemotherapy (CT) is the current standard of treatment for endocrine-resistant metastatic breast cancer (MBC). However, shrinking benefit for consecutive lines of CT and lack of data from randomized trials may question the real value of advanced lines of treatment. Growth modulation index (GMI), the ratio of progression free survival (PFS) with PFS of previous line, has been reported as a marker of treatment benefit when equal to or above 1.3. This value is similar to the clinical benefit threshold proposed by ESMO and ASCO for non-curative CT. The aim of this work was to determine GMI change across the successive lines of CT for MBC.

Methods: We retrospectively analyzed all MBC patients currently on treatment at our center. GMI was determined for each CT line and for each patient and a cut-off value of 1.3 was chosen as a marker of treatment benefit. Chi-squared test and Spearman's Rho were used for proportion comparison and correlations. Kaplan-Meier curves and log-rank test were performed for survival analysis.

Results: 128 ABC patients were included; median age: 57; ECOG 0-1: 92.2%; visceral disease: 46%; bone-only disease: 46.9%; TNBC: 5.5%, HER2+: 23.5%, ER+HER2-: 71.1%; 50% more than 2 lines of CT. GMI and PFS values are shown in Table 1. GMI values were significantly associated with PFS values in all lines (p&lt;0.001 for 2nd, 4th and 5th lines; p&lt;0.01 for 3rd and 6th). GMI was neither significantly different between CT lines nor significantly correlated with GMI of previous line. No consistent association of GMI values with age, performance status, tumor subtype or visceral disease were found.

Table 1. GMI and PFS values for each line of CTCT linenGMI Median (range)GMI ≥ 1.3PFS Median (95%CI)2nd630.88 (0.03-27)36.5%10.4 months (7.2-13.2)3rd390.62 (0.05-7.5)23.1%4.9 months (4.1-5.7)4th280.83 (0.05-12.6)21.4%5.3 months (1.1-9.4)5th200.68 (0.05-9.1)30.0%4.7 months (1.5-7.9)6th140.80 (0.25-22.8)42.9%4.5 months (2.0-7.1)

Conclusions: GMI does not significantly change along successive CT lines for MBC. Our results, showing a constant rate of 20-40% of patients with GMI≥1.3 up to the sixth line of CT, suggest a benefit within the range of magnitude established by ASCO and ESMO framework for cancer care value. Although potential biases of this work warrant further evaluation with a cohort design, GMI, together with toxicity data and absolute gains of PFS, may be used as an additional tool to establish the real value of late lines of CT for MBC.

Citation Format: Ayala de la Peña F, Ivars Rubio A, de la Morena Barrio P, Fernández Sánchez A, Luengo Gil G, García Martínez E, García Garre E, Marín Zafra G, Vicente V. Evaluation of growth modulation index as a marker of benefit for consecutive lines of treatment for metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-15-09.