Type B lactic acidosis is a rare oncological emergency usually associated with leukemia and lymphoma but also with solid malignancies. It can often go unrecognized as a possible source of lactic acidosis, leading to a delay in treatment. We review a 56-year-old woman with systemic lupus erythematosus and generalized lymphadenopathy being evaluated for underlying malignancy who presented with dyspnea, fatigue, and hematemesis. The patient was hemodynamically unstable and had severe lactic acidosis, leukocytosis, electrolyte derangements, multiple organ damage, and worsening diffuse lymphadenopathy. She was initially treated for septic shock due to acalculous cholecystitis on imaging with antibiotics and a cholecystostomy. The latter was complicated by a liver laceration requiring explorative laparotomy and open cholecystectomy, during which an excisional biopsy of the omental lymph node was done and confirmed B-cell lymphoma with marked plasmacytic differentiation. Her lactic acidosis never fully cleared despite surgery, and the refractory nature of it despite appropriate treatment of septic shock confirmed the diagnosis of type B lactic acidosis from underlying B-cell lymphoma. Chemotherapy was deferred due to the acuity of the condition. She continued to deteriorate despite aggressive management and was transitioned to comfort measures only per family request, following which she passed away.Type B lactic acidosis should be suspected in oncology patients without clinical evidence of ischemia who are not responding to fluid resuscitation and appropriate treatment of septic shock. Prompt recognition and early initiation of antineoplastic agents should be considered, when possible, to prevent adverse outcomes.