No more than grade 1 abnormalities of potassium, calcium (confirmed by ionized calcium), magnesium, and phosphorus (supplementation allowed) Uncontrolled hypercalcemia (ionized calcium >1.5 millimoles per liter [mmol/L], calcium >12 milligrams per deciliter [mg/dL], or corrected calcium greater than the upper limit of normal [ULN]) or symptomatic hypercalcemia requiring continued use of bisphosphonate therapy Total serum calcium (corrected for serum albumin) or ionized calcium >= lower limit of normal (LLN) Total and ionized serum calcium outside of normal limits Normal ionized calcium (can be on oral supplementation) Within 14 days prior to registration: Total serum calcium (corrected for serum albumin as needed) or ionized calcium within institution’s normal range Uncontrolled symptomatic hypercalcemia (> 1.5 mmol/L ionized calcium or calcium > 12 mg/dl or corrected serum calcium > ULN) Normal ionized calcium, magnesium and phosphorus (can be on oral supplementation) Current treatment with intravenous bisphosphonate or denosumab with elevated serum calcium corrected for albumin or ionized calcium levels outside institutional normal limits at screening Adjusted (or ionized) calcium >= the institutional lower limit of normal (supplementation of electrolytes prior to screening is allowed) Currently on bisphosphonate or denosumab with elevated serum calcium levels corrected for albumin/ionized calcium levels outside of institutional normal limits Patient has serum potassium and magnesium levels WNL for the institution and total serum calcium or ionized calcium levels ? the lower limit of normal (LLN). Patients with low potassium, calcium, and/or magnesium levels may receive supplementation to meet the protocol entry criteria. (Calcium supplementation is prohibited after starting PBI-05204; see Appendix 2.) Uncontrolled hypercalcemia (greater than [>] 1.5 millimoles per liter [mmol/L] ionized calcium or Ca > 12 milligrams per deciliter [mg/dL] or corrected serum calcium > upper limits of normal [ULN]) or symptomatic hypercalcemia requiring continued use of bisphosphonate therapy or denosumab Electrolytes (including potassium, sodium, and serum calcium corrected for albumin or ionized calcium) must be within normal limits Electrolytes (including potassium, sodium, and serum calcium corrected for albumin or ionized calcium) must be within normal limits Participants with a serum potassium less than 3.5 mmol/L or a serum ionized calcium or magnesium below the lower limits of normal (or above CTCAE grade 1 upper limit); correction of these electrolyte abnormalities with supplements is allowed (serum calcium above the CTCAE grade 1 upper limit; in cases where the serum calcium is below the normal range, the calcium adjusted for albumin is to be obtained and substituted for the measured serum value; exclusion is to then be based on the calcium adjusted for albumin values falling below the normal limit) Total serum calcium [corrected for serum albumin] or ionized calcium >= LLN Patients with normal level of serum ionized calcium and phosphate. Total serum calcium (corrected for serum albumin) or ionized calcium >= LLN Total serum calcium (corrected for serum albumin) or ionized calcium >= LLN Total serum calcium (corrected for serum albumin) or ionized calcium below ULN Total serum calcium or ionized calcium level >= institutional lower limit of normal Current treatment with intravenous bisphosphonate or denosumab with elevated serum calcium corrected for albumin or ionized calcium levels outside institutional normal limits at screening Serum potassium and magnesium levels within institutional normal limits. Total serum calcium or ionized calcium level must be greater than or equal to the lower limit of normal. Serum calcium (ionized or corrected for albumin) ? 2.0 mmol/L (8.0 mg/dL or 1.0 mmol/L ionized calcium) to ? 1.2 x ULN. RECURRENT/ PROGRESSIVE DIPG (STRATUM 1): Serum total calcium (correct for serum albumin) or ionized calcium >= LLN NON-PROGRESSED DIPG (STRATUM 2): Serum total calcium (correct for serum albumin) or ionized calcium >= LLN Total serum calcium (corrected for serum albumin) or ionized calcium >= LLN Total and ionized serum calcium outside of normal limits Total serum calcium [corrected for serum albumin] or ionized calcium >= LLN Serum calcium >=Grade 1 (per CTCAE v4.0) at time of enrolment, unless ionized calcium is within normal range Serum total calcium (corrected for serum albumin) or serum ionized calcium >= LLN Serum calcium (corrected for serum albumin) or ionized calcium >= lower limit of normal (LLN) (treatment of hypercalcemia is allowed and subject may enroll if hypercalcemia returns to normal with standard treatment) Ionized calcium =< ULN Serum calcium above the CTCAE grade 1 upper limit; in cases where the serum calcium is below the normal range, 2 options would be available: 1) the calcium adjusted for albumin is to be obtained and substituted for the measured serum value; exclusion is to then be based on the adjusted for albumin values falling below the normal limit; 2) determine the ionized calcium levels; if these ionized calcium levels are out of normal range despite supplementation, then the patient must be excluded Participants must have an ionized serum calcium within normal limits Patients with hypercalcemia (using ionized calcium)