Severe Pneumonia May Unmask Undiagnosed Blood Cancer in Adults

A Swedish research team has uncovered an unexpected consequence of severe pneumonia: it may be the first visible sign of blood cancer lurking undiagnosed in adults. The finding emerged from a study of 156 patients hospitalized with invasive pneumococcal disease between 2018 and 2023 in Region Västra Götaland, Sweden. The median age was 70 years. When researchers screened these patients for M protein—a biomarker associated with blood cancer risk—they found it in one out of every four.

The discovery matters because what looked like a straightforward infection turned out to be a window into something far more serious. Among the patients who tested positive for M protein, seven received formal diagnoses of blood cancer, and another twelve were found to have precursor conditions with the potential to develop into blood cancer. Eight additional patients were identified as having underlying immunodeficiency, a condition that had gone undetected until the pneumococcal infection brought them to the hospital. Seven of those eight were able to begin preventive treatment to guard against future severe infections. In a matched control group of 64 people without pneumococcal disease, these abnormalities were considerably rarer.

The implication is straightforward but has been largely overlooked in clinical practice. When an adult is hospitalized with severe pneumococcal pneumonia, doctors typically treat the infection and send the patient home. They do not routinely check for M protein or measure antibody levels—the very tests that might reveal an undiagnosed malignancy or immune system failure. Tor Härnqvist, a doctoral student and infectious disease physician at the University of Gothenburg who led the research, put it plainly: "Currently, these tests are not routinely performed after a severe pneumococcal infection. As a result, we may miss patients with undiagnosed blood cancer or immunodeficiency and therefore missing the opportunity to initiate treatment." The study, published in Scientific Reports, suggests that hospitals should consider making M protein and antibody screening standard practice for patients hospitalized with invasive pneumococcal disease.

The research also uncovered a secondary problem that complicates vaccination strategy. After Sweden introduced pneumococcal vaccines into its childhood immunization program, the bacterial strains targeted by that vaccine declined sharply. But nature abhors a vacuum. Those strains were replaced by serotypes not covered by the pediatric vaccine—replacement strains that now circulate widely and disproportionately affect older adults and people with compromised immune systems, including cancer patients. Karin Bergman, another doctoral student and infectious disease physician at Södra Älvsborg Hospital who contributed to the work, noted the policy implication: "The results show that recommendations on pneumococcal vaccines for adults need to take into account which vaccines are used in children and which bacterial serotypes subsequently circulate in the community."

The findings point to a gap in how medicine currently handles severe infections in older patients. A bout of pneumonia that lands someone in the hospital is treated as an acute event, not as a potential diagnostic opportunity. Yet for one in four patients, that infection is the first clinical manifestation of a blood cancer or immune system disorder that has been present all along. The study suggests that closing this gap—by adding two straightforward blood tests to the standard workup for hospitalized pneumococcal disease—could catch cancers and immunodeficiencies early enough to change the course of treatment. At the same time, the shifting landscape of circulating bacterial strains means that adult vaccination recommendations cannot simply remain static; they must evolve in response to what is actually circulating in the community, shaped in part by what children are being vaccinated against.