Guardant Health's stock experienced a significant decline on Thursday following disappointing results from a pivotal study on its second-generation colon cancer test. This drop marked the end of a 67% monthlong increase for Guardant Health's stock, causing concern among investors. The company's shares plummeted as the test did not meet expectations, leading to a negative impact on the company's financial performance. This setback underscores the challenges Guardant Health is facing in the development and commercialization of its advanced diagnostic technologies.