A Study to Find a Suitable Dose of ASP5834 in Adults With Solid Tumors

Inclusion Criteria: * Participant has histologically confirmed locally advanced (unresectable) or metastatic solid tumor malignancy with a documented Kirsten rat sarcoma viral oncogene homolog (KRAS) G12V, G12D, G12C, G12R, G12A or G13D mutation or KRAS amplification (copy number \>/= 4) determined by local testing. * For a participant with a documented KRAS amplification, only those with no other co-occurring KRAS mutation or those with a co-occurring KRAS G12V, G12D, G12C, G12R, G12A or G13D mutation are eligible. * Unique to Europe (EU): Only participants who have pre-existing local results can be enrolled. * For the ASP5834 monotherapy dose escalation part, participant with any histologically confirmed locally advanced (unresectable) or metastatic solid tumor malignancy is eligible. Participant must have received prior standard therapy in the advanced setting, and the investigator does not see any further clinical benefit from continuing such therapy or the participant is ineligible to receive standard approved therapies. * For the ASP5834 monotherapy dose expansion part, the following criteria apply: * \[pancreatic ductal adenocarcinoma (PDAC) Expansion Cohort(s)\] Participant has histologically confirmed locally advanced (unresectable) or metastatic PDAC. * \[PDAC Expansion Cohort(s)\] Participant has a documented KRAS G12V, G12D, G12C, G12R, G12A or G13D mutation determined by local testing. * \[PDAC Expansion Cohort(s)\] Participant must have received standard therapy in the advanced setting, including prior therapy with a gemcitabine-based or fluoropyrimidine-based regimen or is ineligible for these therapies. * \[PDAC Expansion Cohort(s)\] No more than 2 prior lines of systemic therapy are allowed in the advanced setting (note: maintenance therapy does not count as a separate line of therapy). * \[PDAC Expansion Cohort(s)\] For a participant who received prior neoadjuvant or adjuvant chemotherapy and had recurrence on or within 6 months of completion of therapy, the neoadjuvant or adjuvant chemotherapy should be counted as a regimen in the advanced setting. * \[non-small cell lung cancer (NSCLC) Expansion Cohort(s)\] Participant has histologically confirmed locally advanced (unresectable) or metastatic NSCLC. * \[NSCLC Expansion Cohort(s)\] Participant has a documented KRAS G12V, G12D, G12R, G12A or G13D mutation determined by local testing. * \[NSCLC Expansion Cohort(s)\] Participant must have received standard therapy in the advanced setting, including prior platinum-based chemotherapy and checkpoint inhibitor therapy or is ineligible for these therapies. Participants with known actionable genomic alterations (AGA) must have received prior therapy with an approved targeted therapy in accordance with local requirements. * \[NSCLC Expansion Cohort(s)\] For a participant who has received prior neoadjuvant or adjuvant therapy and had recurrence during or within 6 months of completion of therapy, the neoadjuvant or adjuvant therapy should be counted as a regimen in the advanced setting (for those who received perioperative therapy, the entire course should be counted as therapy in the advanced setting). * \[NSCLC Expansion Cohort(s)\] For a participant with a history of unresectable Stage III disease who received prior multi-modal therapy and had recurrence on or within 6 months of completion of therapy, the multi-modal therapy should be counted as a therapy in the advanced setting. If chemoradiation was followed by treatment with checkpoint inhibitor therapy without documented progression between chemoradiation and checkpoint inhibitor therapy, the entire treatment course should be counted as therapy in the advanced setting. * \[Other Solid Tumor Expansion Cohort\] Participant has a histologically confirmed locally advanced (unresectable) or metastatic solid tumor type other than PDAC, colorectal cancer (CRC) or NSCLC. * \[Other Solid Tumor Expansion Cohort\] Participant has a documented KRAS G12V, G12D, G12C, G12R, G12A or G13D mutation or KRAS amplification (copy number \>/=4) determined by local testing. * \[Other Solid Tumor Expansion Cohort\] Participant must have received prior standard therapy in the advanced setting, and the investigator does not see any further clinical benefit from continuing such therapy or is ineligible to receive standard approved therapies. * For ASP5834 combination therapy dose escalation and dose expansion parts, the following criteria apply: * \[CRC Dose Escalation and Dose Expansion Parts\] Participant has histologically confirmed locally advanced (unresectable) or metastatic adenocarcinoma of the colon or rectum. * \[CRC Dose Escalation and Dose Expansion Parts\] Participant has a documented KRAS G12V, G12D, G12C, G12R, G12A or G13D mutation determined by local testing. * \[CRC Dose Escalation and Dose Expansion Parts\] Participant must have received standard therapy in the advanced setting, including prior therapy with fluoropyrimidine, oxaliplatin and irinotecan and anti-vascular endothelial growth factor (VEGF) therapy or is ineligible for these therapies. * \[CRC Dose Escalation and Dose Expansion Parts\] For a participant who has received neoadjuvant or adjuvant chemotherapy and had recurrence during or within 6 months of completion of therapy, the neoadjuvant or adjuvant chemotherapy should be counted as a regimen in the advanced setting. * \[CRC Dose Escalation and Dose Expansion Parts\] Participant with microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) colorectal cancer (CRC) must have also received prior treatment with immune checkpoint inhibitors or is ineligible for these therapies. * Participant consents to provide tumor specimen in a tissue block or unstained serial slides or a baseline tumor biopsy obtained after the last interventional treatment, but not more than 90 days prior to the start of study intervention. Participant also consents to provide a tumor bio