The purpose of this study is to evaluate the investigational oral drug AMXT 1501 in combination with oral eflornithine (DFMO). An investigational drug is one that has not been approved by the U.S. Food \& Drug Administration (FDA), or any other regulatory authorities around the world for use alone or in combination with any drug, for the condition or illness it is being used to treat.

The goals of this part of the study are:

* Establish a recommended dose of AMXT 1501 in combination with DFMO
* Test the safety and tolerability of AMXT 1501 in combination with DFMO
* To determine the activity of study treatments chosen based on:
* How each subject responds to the study treatment
* How long a subject lives without their disease returning/progressing

The purpose of this study is to evaluate the investigational drug, tipifarnib (a pill taken by mouth), in combination with the Food and Drug Administration (FDA) approved drug, naxitimab, administered intravenously (IV; a liquid that continuously goes into your body through a tube that has been placed during a surgery into one of your veins). Naxitamab is FDA approved for pediatric patients 1 year of age and older and adult patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow who have demonstrated a partial response, minor response, or stable disease to prior therapy, it may not be approved in the type of disease used in this study.

The goals of this part of the study are:

* Test the safety and tolerability of tipifarnib in combination with naxitimab in patients with cancer
* To determine the activity of study treatments chosen based on:
* How each subject responds to the study treatment
* How long a subject lives without their disease returning/progressing