The research team followed 156 adults who developed invasive pneumococcal disease and required hospital care in Region Västra Götaland, Sweden, between 2018 and 2023. The median age of the patients was 70 years, a demographic in which both pneumococcal disease and blood malignancies become progressively more common. To determine whether the severe infection was merely bad luck or a signal of hidden vulnerability, the researchers performed detailed immunological workups. They measured antibody levels to detect deficiencies in humoral immunity, and they tested for the presence of M protein, a monoclonal immunoglobulin that serves as a well-established risk marker for blood cancer. A control group of 64 individuals, matched for age and sex but without invasive pneumococcal disease, provided a baseline for comparison.

The results were striking. Among the patients with invasive pneumococcal disease, one in four had M protein detectable in their blood. Monoclonal gammopathy of this kind can occur in established blood cancers, but it is also found in precursor states, conditions that do not yet meet the criteria for malignancy but can, in some patients, progress toward cancer over time. The examinations prompted by the study led to seven patients receiving a diagnosis of blood cancer, while another twelve were diagnosed with a precursor condition that may, in some cases, evolve into malignancy. In a group of just over 150 patients admitted for a severe bacterial infection, that represents a meaningful yield of previously silent disease.

The immune assessments also uncovered antibody deficiencies. Eight patients in the pneumococcal disease group were found to have immunodeficiency, and in seven of them, clinicians were able to start preventive treatment aimed at protecting against future severe infections. Such treatments can include replacement immunoglobulin therapy and tailored vaccination strategies, interventions that can substantially reduce the risk of recurrent invasive disease. By contrast, these abnormalities were considerably less common in the matched control group, reinforcing the idea that invasive pneumococcal infection is not randomly distributed but clusters in people whose immune surveillance is compromised.

The biological logic behind these findings is straightforward once the mechanics of pneumococcal immunity are considered. Streptococcus pneumoniae is an encapsulated bacterium, and its polysaccharide capsule is the principal target of protective antibodies. Clearance of the organism depends heavily on opsonization, the process by which antibodies coat the bacterium and mark it for destruction by phagocytic cells. People with low antibody levels, whether from a primary immunodeficiency or from the antibody-producing B-cell disorders that underlie many blood cancers, are therefore structurally less able to contain the bacterium when it colonizes the respiratory tract. What would be a mild or localized infection in an immunocompetent adult can become a systemic, hospital-requiring illness in someone whose humoral immunity is impaired.

M protein, the marker at the center of the study, is a monoclonal immunoglobulin produced by a single expanded clone of plasma cells or B cells. Its presence in the blood is the hallmark of a spectrum of disorders ranging from the benign-appearing monoclonal gammopathy of undetermined significance to smoldering and symptomatic myeloma. Because monoclonal gammopathies are common in older populations and often remain asymptomatic for years, most are discovered incidentally or not at all. The Gothenburg study suggests that severe pneumococcal disease may function as a clinical flag: when an older adult presents with invasive infection, the probability of finding an underlying monoclonal disorder is high enough that targeted testing could be worthwhile.

Currently, according to the researchers, these tests are not routinely performed after a severe pneumococcal infection. Tor Härnqvist, a doctoral student at the University of Gothenburg and an infectious disease physician at NU Hospital Group, and one of the lead authors of the study, points to the consequence of that gap. “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,” he says. The missed opportunity cuts in two directions: blood cancers such as myeloma are generally more treatable when identified before organ damage accumulates, and immunodeficiencies can be mitigated with preventive measures before the next invasive infection occurs.

The study carries implications for vaccination policy as well. Karin Bergman, a doctoral student in the same research group and an infectious disease physician at Södra Älvsborg Hospital, examined how the pneumococcal bacteria causing severe disease have shifted since the pneumococcal conjugate vaccine was introduced into the Swedish childhood vaccination program. Her analysis, part of a doctoral thesis she will soon defend at the University of Gothenburg, shows that the bacterial serotypes covered by the childhood vaccine have decreased sharply in circulation, but they have largely been replaced by other serotypes against which the childhood vaccine offers no protection. This serotype replacement is a well-documented ecological consequence of conjugate vaccination: eliminating vaccine-targeted strains from nasopharyngeal carriage opens ecological space for non-vaccine strains to colonize and spread.

Crucially, the serotypes now driving invasive disease in adults disproportionately affect older adults and individuals with underlying conditions, particularly cancer and compromised immune systems. This creates an uncomfortable alignment: the very populations most vulnerable to severe pneumococcal infection are those most likely to harbor undiagnosed blood cancer or antibody deficiency, and the circulating bacterial strains are precisely those that exploit gaps in adult immunity. “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,” says Bergman. In other words, adult immunization strategy cannot be designed in isolation from the pediatric program, because the two are epidemiologically linked through the shifting serotype landscape.

Taken together, the findings support a concrete change in clinical practice. The researchers argue that screening for M proteins and antibody levels should be considered in adults who experience invasive pneumococcal disease, since the infection can reveal previously undiagnosed blood cancer and immunodeficiency. Such screening would involve relatively simple blood tests: quantitative measurement of serum immunoglobulins to identify antibody deficiencies, and protein electrophoresis or equivalent methods to detect monoclonal immunoglobulins. For a patient population that is already hospitalized and undergoing extensive workup, the incremental burden would be modest, while the potential benefit, catching a blood cancer or an immune deficiency that would otherwise remain hidden until it caused further harm, could be substantial. As populations age and serotype replacement continues to reshape pneumococcal epidemiology, the severe pneumonia that lands an older adult in the hospital may increasingly deserve to be read not only as an infection, but as a message from the immune system itself.

Subject of Research: Invasive pneumococcal disease as a marker of undiagnosed blood cancer and immunodeficiency in adults

Article Title: Pneumonia can reveal undiagnosed blood cancer

Article References: Pneumonia can reveal undiagnosed blood cancer. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: pneumococcal disease, pneumonia, blood cancer, M protein, immunodeficiency, monoclonal gammopathy, Streptococcus pneumoniae, antibody deficiency, pneumococcal vaccine, serotype replacement, University of Gothenburg, Scientific Reports