Neoplastic diseases during pregnancy present complex diagnostic and therapeutic challenges, requiring a delicate balance between maternal health and fetal safety. Physiological changes of gestation—such as increased plasma volume, hormonal fluctuations, and immunomodulation—can obscure symptoms and delay diagnosis. Breast cancer, cervical cancer, hematologic malignancies, and melanoma constitute the most frequently encountered cancers in pregnancy, each with unique epidemiologic and prognostic features. This chapter reviews current evidence on cancer screening, diagnostic imaging, and biopsy techniques that minimize fetal risk, alongside staging systems adapted for pregnancy. Therapeutic approaches, including surgery, chemotherapy, and radiotherapy, are discussed in relation to gestational age, with emphasis on multidisciplinary decision-making and individualized treatment planning. Special attention is given to timing of delivery, fertility preservation strategies, and ethical considerations in cases where maternal prognosis is poor. By integrating oncologic principles with obstetric care, this chapter aims to provide a comprehensive framework for optimizing outcomes for both mother and child in the context of pregnancy-associated malignancies.