ABSTRACT Background Panitumumab (P-mab) was approved in April 2010 in Japan for treatment of unresectable, advanced or recurrent colorectal cancer with wild-type KRAS, both in monotherapy and in combination with chemotherapy for all lines of treatment. Objectives To investigate the status of post-marketing use and adverse drug reactions (ADRs) of P-mab in Japan, and to assess the safety and efficacy of P-mab in Japanese patients. Methods All-case surveillance (all patients were registered before starting P-mab therapy by the central registration method) was conducted since the product launch. All the patients were examined for eligibility requirements such as KRAS genotype, patient performance status and combination regimen and registered for this study before starting P-mab therapy. Results Between June 2010 until November 2010, 3,091 patients were enrolled. Background information of the 3,005 patients that were collected by October 2011 was as follows: male/female: 1,912/1,093, mean age: 65.0 years (range 18–90), colorectal cancer: 3,005, KRAS genotype wild/ mutant/ not determinable: 2,925/3/77, first line/ second line/third line or later treatment: 312/542/2,150, PS 0-1/2/3/4:2,743/236/22/4 and P-mab monotherapy/combination with chemotherapy: 1,232/1,766. Combination regimens: FOLFOX/ FOLFIRI/ other anticancer agents were 563/1,004/456. Overall incidence of ADRs was 83.7%, Grade 3 or higher ADRs were 24.7%. Incidence of ADRs of special interest for this surveillance: skin disorder / interstitial lung disease/ infusion reaction/ electrolyte abnormality/ cardiac disorder were 77.8%/ 1.3%/ 1.5%/ 18.3%/ 0.2%. The median survival time of patients with P-mab monotherapy as third line treatment was 10.3 months. Conclusion P-mab was administered to patients who met the eligibility requirements and the appropriate use was confirmed. The safety profile of P-mab in the post-marketing use was similar to that previously reported in the clinical trials. The risk/benefit balance for use of P-mab in patients with unresectable colorectal cancer remains favorable. Disclosure K. Sugihara: Membership on advisory board: Takeda, Merck Serono,Chugai Sponsored research and honoraria: Takeda, Taiho, Chugai, Yakult, Bristol-Myers Squibb, Merck Serono, Daiichi-sankyo. Sponsored research: Kyowa Hakko Kirin No other conflict of interest. N. Boku: Membership on advisory board and honoraria: Takeda No other conflict of interest. A. Gemma: Membership on advisory board and honoraria: Takeda No other conflict of interest. N. Yamazaki: Membership on advisory board and honoraria: Takeda, Bristol-Myers Squibb, Merck Serono No other conflict of interest. K. Muro: Membership on advisory board: Takeda Honoraria: Takeda, Yakult, Chugai, Taiho, Bristol-Myers Squibb, Daiichi-sankyo, Merck Serono No other conflict of interest. T. Hamaguchi: Membership on advisory board: Takeda Honoraria: Takeda, Daiichi-sankyo No other conflict of interest. T. Yoshino: Sponsored research: Bayer, Taiho, Daiichi-sankyo,Quintiles Membership on advisory board: Takeda Honoraria: Chugai, Takeda, Bristol-Myers Squibb, Yakult, Merck Serono No other conflict of interest. H. Ueno: Emproyee of Takeda Pharmaceutical Co., Ltd. who sponsored this survey No other conflict of interest. A. Ohtsu: Membership on advisory board,consultant: Takeda, Daiichi-sankyo, Novartis Pharma, Chugai, Taiho Honoraria: Takeda, Daiichi-sankyo, Taiho, GlaxoSmithKline, Pfizer, Yakult, Bristol-Myers Squibb, Merck Serono No other conflict of interest.