Final answer:
Under the same conditions as cultured normal cells, malignant cells do not exhibit contact inhibition and continue to grow and divide, forming multiple layers. This lack of inhibition is due to deficiencies in forming junctions with other cells and attaching to the extracellular matrix, allowing cancer cells to spread and form tumors.
Step-by-step explanation:
Cancer cells, under the same conditions that lead cultured normal cells to exhibit decreased growth rates, do not exhibit contact inhibition. While normal cells stop dividing and form a single layer of cells, cancer cells continue to grow and divide, piling up in multiple layers. This lack of contact inhibition is one of the characteristics of cancer cells, along with deficiencies in forming gap junctions and adherens junctions, and difficulty attaching to an extracellular matrix. These differences in growth between normal and cancer cells contribute to the formation and spread of tumors.