BACKGROUND: Differentiated thyroid cancer is a common endocrine malignancy with an indolent course and high overall survival rate. With more cases diagnosed early, survivors of this cancer live longer and hence are at risk of second primary cancers. In patients with known primary malignancy, work-up often focuses on the primary disease, so that coexistence of another primary malignant lesion can be missed.
CASE PRESENTATION: We report a case of a 78 year-old Filipino male diagnosed to have papillary thyroid cancer with nodal metastases presenting with an incidental rectosigmoid cancer on pre-operative workup.
TREATMENT AND OUTCOME: Patient eventually underwent complete surgical removal of both malignancies. He is currently on levothyroxine suppression therapy with no evidence of tumor recurrence for both malignancy and is on close follow-up for cancer recurrence surveillance.
CONCLUSION: Clinical vigilance for cancer screening and surveillance is mandatory for patients diagnosed with any type of primary malignancy to reduce the rate of missing secondary primary malignancy simultaneously present in the same patient , Early cancer detection might improve cancer patient's overall prognosis and eventually proved to be life-saving.

Human ; Male ; Aged ; Neoplasms ; Patients ; Prognosis ; Thyroxine