Abstract P6-09-07: Mutation characteristics and tumor infiltrating lymphocytes in early and metastatic HER2-positive breast cancer
Authors: Kotoula V , Giannoulatou E , Kouvatseas G , Tikas I , Lazaridis G , Charalambous E , Efstratiou I , Bobos M , Tsolaki E , Zagouri F , Christodoulou C , Pentheroudakis G , Koutras A , Papakostas P , Kosmidis PA , Pectasides D , Fountzilas G 
Published: March 2017

Background-aim: HER2-positive breast cancer (BC) features high rates of tumor infiltrating lymphocytes (TILs) and mutations (mut) in various genes, more frequently in TP53. We investigated associations between TILs and mutations in HER2-positive BC and their impact on patient outcome in early and metastatic BC (EBC and MBC, respectively), which remain largely unexplored.

Methods:In 352 primary paraffin tumors from patients with HER2-positive disease, we examined amino acid changing mutations (&lt;0.1% minor allele frequency) in 58 genes for type and possible clonality (&gt;20% variant frequency). Study groups were: (A) 218 EBC, including 117 patients treated with adjuvant chemotherapy only (CT) and 101 patients treated with CT and trastuzumab (CTT); (B) 134 MBC, including 95 patients who relapsed upon adjuvant CT without trastuzumab (R-MBC) and 39 patients who were first diagnosed with metastatic disease (de novo MBC). TILs were assessed as percentage of stromal tumor area. Clinical endpoints were disease-free survival in 5 years (5yr DFS) for EBC, and time-to-progression (TTP) from 1st line CTT treatment start for MBC.

Results: 243/352 tumors (69%) carried at least one mut; 27/352 (8%) of tumors &gt;10 up to 150 mut (hypermut); 192/352 (54%) at least one possibly clonal mut. Mean mut number and TP53 mut in particular were highest in R-MBC and lowest in EBC; mean TILs density followed the opposite pattern (all p&lt;0.001). TILs density was lower in all settings in hypermut tumors and in tumors with multiple clonal mut (p values 0.043 – 0.050). Upon multivariate analysis in EBC, higher risk for relapse in 5yrs was noticed for CT patients compared to CTT (odds ratio [OR] 2.39, 95%CI [CI] 1.13-5.04, p=0.023) and for &gt;3 compared to 0-3 positive nodes (OR 3.83, CI 1.76-8.34, p=0.001); lower risk for relapse was observed for higher TILs irrespectively of treatment (OR 0.93, CI 0.90-0.97, p=0.001), for TP53 mut (OR 0.39, CI 0.18-0.87, p=0.022) and for clonal TP53 mut in CTT-treated patients (OR 0.10, CI 0.02-0.58) but not in CT-treated patients (interaction p=0.084). The presence of any clonal mut (hazard ratio [HR] 2.77, CI 1.42-5.38) and of clonal TP53 mut (HR 2.24, CI 1.20-4.17) conferred worse TTP in de novo but not in R-MBC; these interactions remained significant upon multivariate analysis (interaction p=0.007 and p=0.061, respectively). Higher TILs in the absence of clonal mut conferred longer TTP (HR 0.75, CI 0.56-0.99) but no such effect was observed for tumors with clonal mut (multivariate interaction p=0.052). Classic independent predictors of unfavorable TTP in MBC were younger age (p=0.002), absence of hormone receptors (p=0.001) and poor performance status (p=0.044). PIK3CA mut did not remain significant in any of the examined settings.

Conclusions: The expected pattern of higher TILs associated with mutation number and clonality was not observed in HER2-positive BC; the favorable effect of TILs only in the absence of clonal mut in MBC may imply exhausted immune response. Clonal TP53 mut may serve as a predictor for trastuzumab benefit in EBC but as an adverse prognosticator in trastuzumab-treated de novo MBC, which, if further validated, is of potential clinical relevance.Background-aim: HER2-positive breast cancer (BC) features high rates of tumor infiltrating lymphocytes (TILs) and mutations (mut) in various genes, more frequently in TP53. We investigated associations between TILs and mutations in HER2-positive BC and their impact on patient outcome in early and metastatic BC (EBC and MBC, respectively), which remain largely unexplored.

Methods:In 352 primary paraffin tumors from patients with HER2-positive disease, we examined amino acid changing mutations (&lt;0.1% minor allele frequency) in 58 genes for type and possible clonality (&gt;20% variant frequency). Study groups were: (A) 218 EBC, including 117 patients treated with adjuvant chemotherapy only (CT) and 101 patients treated with CT and trastuzumab (CTT); (B) 134 MBC, including 95 patients who relapsed upon adjuvant CT without trastuzumab (R-MBC) and 39 patients who were first diagnosed with metastatic disease (de novo MBC). TILs were assessed as percentage of stromal tumor area. Clinical endpoints were disease-free survival in 5 years (5yr DFS) for EBC, and time-to-progression (TTP) from 1st line CTT treatment start for MBC.

Results: 243/352 tumors (69%) carried at least one mut; 27/352 (8%) of tumors &gt;10 up to 150 mut (hypermut); 192/352 (54%) at least one possibly clonal mut. Mean mut number and TP53 mut in particular were highest in R-MBC and lowest in EBC; mean TILs density followed the opposite pattern (all p&lt;0.001). TILs density was lower in all settings in hypermut tumors and in tumors with multiple clonal mut (p values 0.043 – 0.050). Upon multivariate analysis in EBC, higher risk for relapse in 5yrs was noticed for CT patients compared to CTT (odds ratio [OR] 2.39, 95%CI [CI] 1.13-5.04, p=0.023) and for &gt;3 compared to 0-3 positive nodes (OR 3.83, CI 1.76-8.34, p=0.001); lower risk for relapse was observed for higher TILs irrespectively of treatment (OR 0.93, CI 0.90-0.97, p=0.001), for TP53 mut (OR 0.39, CI 0.18-0.87, p=0.022) and for clonal TP53 mut in CTT-treated patients (OR 0.10, CI 0.02-0.58) but not in CT-treated patients (interaction p=0.084). The presence of any clonal mut (hazard ratio [HR] 2.77, CI 1.42-5.38) and of clonal TP53 mut (HR 2.24, CI 1.20-4.17) conferred worse TTP in de novo but not in R-MBC; these interactions remained significant upon multivariate analysis (interaction p=0.007 and p=0.061, respectively). Higher TILs in the absence of clonal mut conferred longer TTP (HR 0.75, CI 0.56-0.99) but no such effect was observed for tumors with clonal mut (multivariate interaction p=0.052). Classic independent predictors of unfavorable TTP in MBC were younger age (p=0.002), absence of hormone receptors (p=0.001) and poor performance status (p=0.044). PIK3CA mut did not remain significant in any of the examined settings.

Conclusions: The expected pattern of higher TILs associated with mutation number and clonality was not observed in HER2-positive BC; the favorable effect of TILs only in the absence of clonal mut in MBC may imply exhausted immune response. Clonal TP53 mut may serve as a predictor for trastuzumab benefit in EBC but as an adverse prognosticator in trastuzumab-treated de novo MBC, which, if further validated, is of potential clinical relevance.

Citation Format: Kotoula V, Giannoulatou E, Kouvatseas G, Tikas I, Lazaridis G, Charalambous E, Efstratiou I, Bobos M, Tsolaki E, Zagouri F, Christodoulou C, Pentheroudakis G, Koutras A, Papakostas P, Kosmidis PA, Pectasides D, Fountzilas G. Mutation characteristics and tumor infiltrating lymphocytes in early and metastatic HER2-positive 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 P6-09-07.