Cancer is caused by genetic changes controlling cell progression and differentiation. These changes are unregulated when tumours advance and acquire invasive and metastatic capacities due to the innate biologic characteristics of the cancer cell. In vivo and in vitro models show that these molecular changes are crucial for tumour development and survival. These molecular changes can be used to develop pristine cancer treatments. New methodological molecules are being developed to identify cancer-specific modifications in proteins, DNA, and RNA, as well as molecular distinctions between healthy and cancer cells. This approach enables effective early detection, precise diagnosis, and quick cancer therapy. DNA microarray techniques have been developed for identifying cancer-associated mutations and gene profiles. Molecular cancer diagnostics need improvement alongside advances in genomics, precision medicine, and immunotherapy. This chapter discusses different molecular diagnostics in the evaluation of cancers.