<div><div></div><div>Heidelberg Pharma AG/ Key word(s): Scientific publication Heidelberg Pharma to Present Data from its ADC Technology Platform at AACR Annual Meeting 2026 04.04.2026 / 10:07 CET/CESTThe issuer is solely responsible for the content of this announcement.PRESS RELEASEHeidelberg Pharma to Present Data from its ADC Technology Platform at AACR Annual Meeting 2026 Ladenburg, Germany, 4 April 2026 – Heidelberg Pharma AG (FSE: HPHA), a clinical-stage biotech company developing innovative Antibody Drug Conjugates (ADCs), will present promising preclinical data from its Amanitin-based ADC HDP-103 targeting metastatic castration‑resistant prostate cancer (mCRPC) at the American Association of Cancer Research (AACR) Annual Meeting 2026 in San Diego, California, USA, from 17 to 22 April.AACR Annual Meeting 2026Details of the conference and poster presentation are as follow:Poster: HDP-103, a PSMA targeting amanitin-based ADC, is efficacious even in difficult to treat patient derived xenograft models with heterogenous PSMA expression<div><table><tbody><tr><td>Poster number:</td><td>5639</td></tr><tr><td>Session:</td><td>Antibody-Drug Conjugates and Linker Engineering 4</td></tr><tr><td>Presentation time:</td><td>21 April, 2:00 pm – 5:00 pm PDT</td></tr><tr><td>Link to abstract:</td><td>https://www.abstractsonline.com/pp8/#!/21436/presentation/5438</td></tr></tbody></table></div>HDP-103 demonstrates target specific binding in human tissues and robust and durable antitumor activity in patient-derived xenograft (PDX) models representative of mCRPC, including tumors with heterogeneous PSMA expression and those harboring a del(17p). In these models, Amanitin-based HDP-103 was superior to an anti-PSMA Exatecan ADC. Adverse events with HDP-103 in non-human primates were restricted to known off-target effects of Amanitin-based ADCs, primarily in the liver and kidney. These effects can be readily monitored and are transient. HDP-103 serum levels demonstrate stability of the ADC in circulation, no evidence of drug accumulation, no differences between sexes, and dose-linearity.The potent anti-tumor efficacy of HDP-103 combined with a favorable half-life and a manageable safety profile, leads to a comfortable therapeutic index (TI) of HDP-103 that is well in the range of other ADCs that are approved or in development for solid tumor indications. Taken together, these data warrant further clinical development of HDP-103 as a novel treatment option for mCRPC. HDP-103´s unique mode of action gives it advantages over other treatment modalities in use or development for mCRPC including in patients with del(17p) who have a high unmet medical need.About Heidelberg PharmaHeidelberg Pharma is the first company to develop cancer therapies using Amanitin, a compound derived from the green death cap mushroom. The biological mechanism of action of the toxin represents a new therapeutic modality and is used as a compound in the Amanitin-based ADC technology, the so-called ATAC technology.Lead candidate HDP-101 (INN: pamlectabart tismanitin) is a BCMA ATAC in clinical development for multiple myeloma. The candidate has been granted Orphan Drug Designation and Fast Track Designation from the FDA. A second ATAC candidate, HDP-102 is in clinical development stage in Non-Hodgkin Lymphoma. HDP-103 against metastatic castration-resistant prostate cancer and HDP-104 targeting gastrointestinal tumors such as colorectal cancer have completed preclinical development. These programs are available for partnering.The company is based in Ladenburg, Germany, and is listed on the Frankfurt Stock Exchange: ISIN / WKN A11QVV / Symbol HPHA. More information is available at www.heidelberg-pharma.comATAC® is a registered trademark of Heidelberg Pharma Research GmbH.<ul><li>Contact Heidelberg Pharma AG Sylvia WimmerSenior Director Corporate CommunicationsTel.: +49 6203 1009 1004E-mail: investors@hdpharma.comGregor-Mendel-Str. 22, 68526 Ladenburg</li><li>IR/PR-Support MC Services AGKatja Arnold (CIRO) Managing Director &amp; PartnerTel.: +49 89 210 228-40E-mail: katja.arnold@mc-services.eu </li></ul>This communication contains certain forward-looking statements relating to the Company's business, which can be identified by the use of forward-looking terminology such as &#34;estimates&#34;, &#34;believes&#34;, &#34;expects&#34;, &#34;may&#34;, &#34;will”, &#34;should”, &#34;future&#34;, &#34;potential&#34; or similar expressions or by a general discussion of the Company's strategy, plans or intentions. Such forward-looking statements involve known and unknown risks, uncertainties and other factors, which may cause our actual results of operations, financial condition, performance, achievements, or industry results, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Given these uncertainties, prospective investors and partners are cautioned not to place undue reliance on such forward-looking statements. We disclaim any obligation to update any such forward-looking statements to reflect future events or developments. 04.04.2026 CET/CEST Dissemination of a Corporate News, transmitted by EQS News - a service of EQS Group.The issuer is solely responsible for the content of this announcement.The EQS Distribution Services include Regulatory Announcements, Financial/Corporate News and Press Releases. <div><table><tbody><tr><td>Language:</td><td>English</td></tr><tr><td>Company:</td><td>Heidelberg Pharma AG</td></tr><tr><td></td><td>Gregor-Mendel-Str. 22</td></tr><tr><td></td><td>68526 Ladenburg</td></tr><tr><td></td><td>Germany</td></tr><tr><td>Phone:</td><td>+49 (0) 89 41 31 38 - 0</td></tr><tr><td>Fax:</td><td>+49 (0) 89 41 31 38 - 99</td></tr><tr><td>E-mail:</td><td>investors@hdpharma.com</td></tr><tr><td>Internet:</td><td>www.heidelberg-pharma.com</td></tr><tr><td>ISIN:</td><td></td></tr><tr><td>WKN:</td><td>A11QVV</td></tr><tr><td>Listed:</td><td>Regulated Market in Frankfurt (Prime Standard); Regulated Unofficial Market in Dusseldorf, Munich, Stuttgart, Tradegate BSX</td></tr><tr><td>EQS News ID:</td><td>2303834</td></tr></tbody></table></div><div><table><tbody><tr><td colspan="2"> </td></tr><tr><td>End of News</td><td>EQS News Service</td></tr></tbody></table></div>2303834 04.04.2026 CET/CEST <section>Disclaimer<div>Saving the news in databases or any forwarding of the news to third parties in a commercial context or for commercial purposes is only permitted with the prior written consent of EQS Group AG.</div></section></div></div>

Heidelberg Pharma AG will present preclinical data on its Amanitin-based ADC HDP-103 at the AACR Annual Meeting 2026, targeting metastatic castration-resistant prostate cancer. The presentation will showcase the ADC's efficacy in challenging patient-derived xenograft models and its favorable safety profile. The company, based in Ladenburg, Germany, is developing innovative cancer therapies using Amanitin and has other ADC candidates in clinical development. The meeting will take place from April 17 to 22, 2026, in San Diego, California.