It has long been postulated that the use of modularity in assurance cases has the potential to bring extensive benefits through its ability to manage technical and organisational complexity, provide a scalable solution and facilitate re-use in future large complex systems. Previous work such as that undertaken by the Industrial Avionics Working Group (IAWG), has shown how a modular assurance case approach could be adopted for real systems, however despite this, its uptake by industry has been slow. The Object Management Group,(OMG), recently published Version 2.1 of their standard for assurance cases, called the Structured Assurance Case Metamodel (SACM). By providing a standardised metamodel for assurance cases, SACM also supports the integration and interchange of different assurance artifacts and controlled terminology. This makes SACM the ideal mechanism to support modular assurance cases through the development of assurance case packages, interfaces and integration bindings. In this paper we describe the state of the art for modular assurance cases through an example from the IAWG project, expressed using the modular GSN notation. We show how this example could be developed using SACM. We go on to discuss the key challenges that are preventing the wide-spread adoption of modular assurance cases and discuss the extent to which SACM may be able to help address these challenges.