A genome-wide association study identifies three novel genetic markers for response to tamoxifen: A prospective multicenter study

Purpose

Although association studies of genetic variations with the clinical outcomes of breast cancer patients treated with tamoxifen have been reported, genetic factors which could determine individual response to tamoxifen are not fully clarified. We performed a genome-wide association study (GWAS) to identify novel genetic markers for response to tamoxifen.

Experimental design

We prospectively collected 347 blood samples from patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative, invasive breast cancer receiving preoperative tamoxifen monotherapy for 14 to 28 days. We used Ki-67 response in breast cancer tissues after preoperative short-term tamoxifen therapy as a surrogate marker for response to tamoxifen. We performed GWAS and genotype imputation using 275 patients, and an independent set of 72 patients was used for replication study.

Results

The combined result of GWAS and the replication study, and subsequent imputation analysis indicated possible association of three loci with Ki-67 response after tamoxifen therapy (rs17198973 on chromosome 4q34.3, rs4577773 on 6q12, and rs7087428 on 10p13, P_combined = 5.69 x 10⁻⁶, 1.64 x 10⁻⁵, and 9.77 x 10⁻⁶, respectively). When patients were classified into three groups by the scoring system based on the genotypes of the three SNPs, patients with higher scores showed significantly higher after/before ratio of Ki-67 compared to those with lower scores (P = 1.8 x 10⁻¹²), suggesting the cumulative effect of the three SNPs.

Conclusion

We identified three novel loci, which could be associated with clinical response to tamoxifen. These findings provide new insights into personalized hormonal therapy for the patients with breast cancer.

Abstract 2031: Association between CYP2D6 genotype and response to tamoxifen in a prospective multicenter study in Japan

Purpose:

CYP2D6 is key enzyme responsible for the generation of the potent active metabolite of tamoxifen, “endoxifen”. We previously reported that reduced- or null-function alleles of CYP2D6 were significantly associated with poor clinical outcome of breast cancer patients treated with tamoxifen. However, there are still discrepant reports questioning the association between CYP2D6 genotype and tamoxifen efficacy. Hence, we carried out prospective multicenter studies to evaluate the value of CYP2D6 genotyping in tamoxifen therapy.

Patients and Methods:

We studied 279 patients with hormone receptor-positive and Her-2 negative, invasive breast cancer receiving preoperative tamoxifen monotherapy for 14 - 28 days. Ki-67 response in breast cancer tissues after tamoxifen therapy was used as a surrogate marker of response to tamoxifen. We investigated the effects of allelic variants of CYP2D6 on Ki-67 change in breast cancer tissues, histological response, breast conservative operation and hot flash.

Results:

Ki-67 labeling index in breast cancer tissues significantly decreased after preoperative tamoxifen monotherapy for 14-28 days (P = 0.00000000024). Moreover, proportion of estrogen receptor positive cells in breast cancer tissues were significantly associated with Ki-67 change after tamoxifen therapy (P = 0.0099). CYP2D6 variants were not significantly associated with histological response, breast conservative operation and hot flash (P = 0.25, P = 0.28 and P = 0.34, respectively). However, CYP2D6 variants were significantly associated with Ki-67 decrease after the preoperative tamoxifen therapy (P = 0.000014; in patients with two variant alleles v patients carrying one or two wild-type alleles).

Conclusion:

Our result suggest that genetic variation in CYP2D6 is a key predictor for the prognosis of patients with breast cancer treated with tamoxifen.

Citation Format: Hitoshi Zembutsu, Seigo Nakamura, Sadako Akashi-Tanaka, Takashi Kuwayama, Chie Watanabe, Tomoko Takamaru, Hiroyuki Takei, Kana Miyahara, Hiroshi Matsumoto, Yoshie Hasegawa, Goro Kutomi, Hiroaki Shima, Fukino Satomi, Hideki Maeda, Minoru Okazaki, Hisamitsu Zaha, Mai Onomura, Ayami Matsukata, Yasuaki Sagara, Shinichi Baba, Akimitsu Yamada, Kazuhiro Shimada, Daisuke Shimizu, Koichiro Tsugawa, Arata Shimo, Tan Ern Yu, Mikael Hartman, Chan Ching Wang, Soo Chin Lee, Yusuke Nakamura. Association between CYP2D6 genotype and response to tamoxifen in a prospective multicenter study in Japan. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2031.

Abstract 5482: CYP2D6 genotype and response to neoadjuvant tamoxifen therapy: a prospective study in Japan

Although lots of CYP2D6-Tamoxifen studies have been reported, the results of the association are still controversial. Because prospective studies are necessary to fully establish the value of CYP2D6 genotyping in tamoxifen therapy, we have initiated the prospective study to clarify the relationship between CYP2D6 genotype and response to preoperative Tamoxifen therapy using a surrogate marker of Ki-67 labeling index in cancer tissue (C-GENT study) since July, 2012. Of the 342 patients who have been recruited in this study, we analyzed 173 cases whose genotyping and measurement of Ki-67 Labeling Index were completed. We observed significant Ki-67 decrease after 2-4 weeks preoperative Tamoxifen therapy (P = 0.000052). Moreover, the patients with CYP2D6 *V/*V is unlikely to show Ki-67 decrease compared with those with CYP2D6 Wt/Wt or Wt/*V (P = 0.00046). Although further analysis should be continuing using a larger number of samples registered in this study, our results suggested that polymorphisms in CYP2D6 could be a key predictor for the prognosis of patients with breast cancer treated with tamoxifen.

Citation Format: Hitoshi Zembutsu, Seigo Nakamura, Sadako Akashi, Takashi Kuwayama, Chie Watanabe, Hiroyuki Takei, Takashi Ishikawa, Yoshie Hasegawa, Soo Chin Lee, Tan Ern Yu, Ayami Matsukata, Hiroshi Matsumoto, Goro Kutomi, Yusuke Nakamura. CYP2D6 genotype and response to neoadjuvant tamoxifen therapy: a prospective study in Japan. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5482. doi:10.1158/1538-7445.AM2015-5482

[A patient with of metastatic breast cancer with a well-controlled quality of life using S-1 therapy as first-line chemotherapy]

We experienced a case of endocrine therapy-resistant recurrent breast cancer with liver and bone metastases, treated with S-1 as first-line chemotherapy and maintaining a good quality of life. The patient was a 31-year-old premenopausal woman. She was diagnosed with cancer of the left breast(T1(18mm), N0, M(-))and underwent breast-conserving surgery, sentinel lymph node biopsy, and radiation therapy in August 2002. As there was hormone sensitivity, she was treated with LHRH analog for 3 years and tamoxifen for 5 years as adjuvant therapy. After her first childbirth, she had a recurrence of liver and bone metastases. After treatment with endocrine therapy failed, an oral administration of S-1 was initiated as first-line chemotherapy considering her QOL. She received 8 months of S-1 therapy with no severe adverse reactions and maintained a high quality of life. Treatment with S-1 is thought to be useful for first-line chemotherapy if the treatment demonstrates a therapeutic equivalence with taxane on patients' overall survival.