Which of the following could indicate a serious underlying condition in a patient with cervical lymphadenopathy?

Painless rubbery lymph nodes and the presence of systemic symptoms such as fever and night sweats can signal a potentially serious underlying condition. Painless, rubbery lymph nodes may suggest malignancies such as lymphoma or metastatic cancer, as these characteristics are often associated with neoplastic processes. On the other hand, fever and night sweats can indicate systemic illnesses, including infections like tuberculosis or HIV, as well as malignancies.

When both of these presentations occur together, they raise the suspicion for malignancy or a significant infectious process that warrants further investigation. Therefore, the combination of painless lymph nodes (characteristic of serious conditions) along with systemic symptoms like fever and night sweats effectively indicates the possibility of a serious underlying condition, justifying the choice of both those indicators.